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What changed my mind to be in favor of TLS inspection at work environments was seeing what kind of highly confidential stuff employees might be copy-pasting to random websites, LLM assistants, cloud-based "desktop applications" and such against the approved use policies of each of these tools without giving it a second thought.

TLS inspection products can intercept the paste transaction before the data leaves the company network, hitting the user with a "No you didn't! Shame on you!"-banner and notify the admins how a user just tried to paste hundreds of customers' personal information and credit card details into some snooping website, or into otherwise allowed LLM chat which still is not allowed to be used with confidential information.

There can even be automations to lock the user/device out immediately if something like this is going on, be it the user or some undetected malware in the user's device attempting the intercepted action. Being able to do these kinds of very specifically targeted interceptions can prevent potentially huge disasters from happening while still allowing users more freedom in taking advantage of the huge variety of productivity tools available these days. No need to choose between completely blocking all previously unseen tools or living in fear of disastrous leaks when there are fine-grained possibilities to control what kind of information can be fed to the tools and from where.

There are plenty of organizations out there where it is completely justified to enforce such limitations and monitoring in company devices. Policies can forbid personal use entirely where it is deemed necessary and legal to do so. Of course the policies and the associated enforced monitoring needs to be clearly communicated and there needs to be carefully curated configurations to control where and how TLS is or isn't intercepted so employee privacy laws and regulations aren't breached either.

One thing that has not quite been mentioned in the blog, is how much of the MITM spyware comes from very big and well known „security“ companies.

You know, the ones that really know about security. X-PAN-AUTHCHECK type of security.

The amount of CVEs some of the big firewall companies collect make it seem like it is a competition for the poorest security hygiene.

The real problem we have is compliance theatre where someone in management forces these solutions onto their IT department just so they can check a box on their sheets and shift all responsibilities away.

Complains about TLS inspection, yet fronts their website on the biggest and most widely deployed TLS introspection middle box in the world ...

Why do we all disdain local TLS inspection software yet half the Internet terminates their TLS connection at Cloudflare who are most likely giving direct access to US Intelligence?

It's so much worse as it's infringing on the privacy and security of billions of innocent people whilst inspection software only hurts some annoying enterprise folks.

I wish we all hopped off the Cloudflare bandwagon.

I agree with the sentiment, but I think it's a pretty naive view of the issue. Companies will want all info they can in case some of their workers does something illegal-inappropiate to deflect the blame. That's a much more palpable risk than "local CA certificates being compromised or something like that.

And some of the arguments are just very easily dismissed. You don't want your employer to see you medical records? Why were you browsing them during work hours and using your employers' device in the first place?

> Consider this - what is the likelihood of every certificate authority on the Internet having their private keys compromised simultaneously? I’d wager that’s almost at the whatever is the statistics equivalent of the Planck length level of probability.

It doesn't matter if every certificate authority is compromised or just one. One is all that is needed to sign certificates for all websites.

Companies know that it's important to have Cybersecurity™. A vendor shows up with shiny brochures, and company is happy to purchase Cybersecurity™.

Now they don't have to worry about it anymore, they bought a product that sits in the corner and delivers Cybersecurity™

> Consider this - what is the likelihood of every certificate authority on the Internet having their private keys compromised simultaneously?

Considering that CloudFlare has managed to MitM a huge part of the internet, I'd say that probability is not just non-zero, but greater than by a worrying margin.

Our cyber team have installed zscaler on most people's laptop, and somewhere in the fabric of the office internet connection.[1]

For those that don't know, its a MITM proxy with certificates so that it can inspect and unroll TLS traffic.

ostensibly its there to stop data exfiltration, as we've had a number of incidents where people have stolen data and sent it to competitors. (our c-suite don't have as much cyber shit installed, despite them being the ones that are both targets more, and broken the rules more....)

Now, I don't like zscaler, and I can sorta see the point of it. But.

Our cyber team is not a centre of technical excellence. They somehow managed to configure zscaler to send out the certs for a random property company, when people were trying to sign into our VPN.

this broke loads of shit and made my team (infra) look bad. The worrying part is they still haven't accepted that serving a random property company's website cert instead of our own/AWS's cert is monster fuckup, and that we need to understand _why_ that happened before trying anything again.

[1] this makes automatic pen testing interesting because everything we scan has vulnerabilities for NFS/CIFS, FTP and TCP dns.

This is why I don't use the computers at work for anything not work related. They've been spying on us for at least 10 years.

I largely agree with the author. When our SOC wanted to implement TLS inspection I blocked it. Mostly because we not nearly at the security level for this, but also because it just fucks with so many things.

That said, we are not a business dealing with highly sensitive data or legal responsibilities surrounding data loss prevention.

If you are a business like that, say a bank or a hospital, you want to be able to block patient / customer data leaving your systems. You can do this by setting up a regex for a known format like patient numbers or bank account numbers.

This requires TLS inspection obviously.

Though this makes it harder to steal this data, not impossible.

It does however allow the C-suite to say they did everything they could to prevent it.

I'm hoping this doesn't apply to things like Fiddler, because without the ability to see what's actually coming over the wire with a https connection, things can be a nightmare to debug sometimes

a company, I worked for, had their own endpoint which you can easily introduce in windows, unfortunately every other tls connection which does not use the windows certificate store breaks because of that, so maven, npm et al won't work

Hey, allowing your employees to have secure connection to websites shows up in red in some Excel spreadsheet. We can't have Excel spreadsheets showing red in fintech. /s

As a sysadmin I also hate this. Instead, I do block stuff based on DNS requests and I also block any other DNS provider as well as malicious IPs.

At this point in time, Microsoft is the bigger enemy here - some of their policies are just insane and none of this MITM will help [0][1]

[0] https://www.microsoft.com/en-us/microsoft-365/roadmap?id=490...

[1] https://techcommunity.microsoft.com/blog/microsoft365copilot...

It's definitely annoying if you work in enterprise, but on the flip side: the fact that these enterprise requirements exist is the main reason that TLS certificate configurability is possible at all, without which it would be dramatically harder (or impossible) to reverse engineer or do security & privacy research on mobile apps, IoT, etc etc etc.

Enterprise control over company devices and user control over personal devices are not so different.

A few apps do use certificate pinning nowadays, which creates similar problems, but saying "you can never add your own MitM TLS cert" is not far from certificate pinning everything everywhere all the time. Good luck creating a new home assistant integration for your smart airfryer when you can't read any of the traffic from its app.

Imo: let's make it easier! Standardize TLS configuration for all tools, make easy cert configuration of devices a legal requirement (any smart device sold with hardcoded CA certificates is a device with a fixed end date, where the CA certs expire and it becomes a brick), guarantee user control over their own TLS trust, and provide good tools to check exactly who you're trusting (and expose that clearly to users). Not really practical of course (and opens all sorts of risky games with nation state interception as well) but there are upsides here as well.

This kind of TLS "man in the middle" tech is so frustrating to deal with, because it ends up breaking things.

For example, I've encountered zscaler setups in the wild which close TLS connections if non-HTTP traffic is encountered. Presumably the traffic inspection fails since there is no HTTP request, and this failure path closes the socket.

It's hard to say whether it's due to the customer's IT dept's config, or zscaler itself -- but as far as the customer is concerned, it's my problem.

Lame on user machines, but sometimes needed in a server environment. Easier to detect if someone is hauling off with your database as that will be the one you can’t see what’s going on. Of course, solve one problem and introduce three more.

The fact that most tools have completely different ways to allow them to add certificates is the biggest pain. Git, Python and Rust also have large issues. Git doesn't default to "http.schannel". Python (or rather requests, or maybe urllib3) only looks at its own certificate store, and I have no idea how Rust does this (well, I use uv, and it has its own problems - I know about the --use-native-tls flag, but it should be a default at the least).

I really wish more places would enable explicit proxies: if you have a mandate to inspect all traffic, block 443 except to proxy.megacorp.com and configure clients to use it. You lose all of the bugs and security issues caused by the security software—fun fact, Palo Alto _still_ doesn’t correctly implement TLS 1.2!—which as the author points out is basically training users to disable validation or ignore errors. This is so common I’ve seen security people with the usual certs giving advice from ChatGPT to add -k to curl calls, which is especially great when that’s baked into a container which will run on other networks.

One really nice win is troubleshooting: inspection appliances break decades of performance and reliability work which groups like the Linux kernel developers have done, and they make all errors have the same symptom so the security team will now be the only people who can troubleshoot network-level issues. Explicit proxying can’t fix your network but it makes it very clear where the problem needs to be investigated.

I remember at my first job, the internet stopped working at my workstation. I got on the phone with IT, and the guy said "looks like you don't have our new certificates." I asked why I would need my employer's certificates. He said "because we MITM every connection." I asked if that was even legal, and he said yes it's legal.

At another job I was handling a support ticket where a customer was asking, in so many words, "can I get HTTP headers of requests flowing through my Envoy TLS reverse proxy?" I said that they could terminate TLS at the proxy and redo things that way, but then that wouldn't be a TLS proxy it'd be a MITM or a gateway. They could log the downstream/upstream and duration of connections, but that wouldn't help.

Isn't the accepted risk of losing all the digital keys equal to the risk of someone booting up the root CA and walking away with it? I can see that happening in a junta situation.

https://www.iana.org/dnssec/ceremonies

zScaler is a load of shit, especially with some of its absolutely dumb policies like “malicious TLDs”.

Because the Framework laptop site at frame.work is malicious, of course.

God, I love CURLing crap from my workstation and not getting the files I needed but instead a bunch of mangled HTML telling me zScaler was going to scan what I was going to download.

Bonus points that it puts me in the wrong country because I’m closer to Montreal than any American locations so half the time I’m stuck in French Canadian on the web from my New York office.

Triple bonus points that I’m required to test speed at client sites and zScaler completely mangles our presentable results.

Quadruple bonus points that I put in "because I feel like it" into every elevation request I make on my corporate machine and our "cyber team" has literally never looked at elevation reports to ask what the hell I'm doing...

But I need to see what they are googling! /sarcasm

The author is complaining a lot about implementation pains without taking a step back and looking at why it exists in the first place.

Say you work at a place that deals with credit cards. You, as a security engineer, have a mandate to stop employees from shipping CC numbers outside the org.

You can educate all you want, you can have scary policies and HR buy-in, you can have all the "Anomaly detection, Zero Trust network architecture, EDR, Netflow analysis" in the world, but exactly zero of those will stop Joe Lunchbox from copy/pasting a block with a CC number in the middle into ChatGPT. You know what will? A TLS-inspecting proxy with some DLP bits and bobs.

It sucks, yes. But it works, and (short of the fool's errand of trying to whitelist every site any employee needs) it's the only thing that works.

And yes, I'm aware PCI DSS has additional requirements for CDEs and whatnot, but really this can apply to anything -- a local government office dealing with SSNs, a school with student ID numbers, a corporation with trade secrets.. these problems exist everywhere, and implementing PCI-like controls is often a bridge too far for unregulated industries.

personally i'm happy that i can MITM my docker when it wants to pull gigs of images the 1000th time upstream and just serve them from a local OCI cache server instead.

The title should say "Stop inspecting TLS", the current title reads like the TLS standard or technology is modified in a way to not work properly.

I agree with the sentiment, but this part is complete bullshit:

> what is the likelihood of every certificate authority on the Internet having their private keys compromised simultaneously

Who cares? It's not like all CAs would have to be breached, just one. CA certs are not scoped, so the moment one CA gets breached, we're all fucked. CT helps, but AFAIK it's still not enforced everywhere yet

Honestly, the author is spot on about the normalisation problem. I've watched this play out at multiple organisations. You implement TLS inspection, spend ages getting certs deployed, and within six months `curl -k` is in half your runbooks because "it's just the corporate proxy again".

He's also absolutely right about the architectural problems too, single points of failure, performance bottlenecks, and the complexity in cloud-native environments.

That said, it can be a genuinely valuable layer in your security arsenal when done properly. I've seen it catch real threats, such as malware C2 comms, credential phishing, data exfiltration attempts. These aren't theoretical; they happen daily. Combined with decent threat intelligence feeds and behavioural analytics, it does provide visibility that's hard to replicate elsewhere.

But, and this is a massive but, you can't half-arse it. If you're going to do TLS inspection, you need to actually commit:

Treat that internal CA like it's the crown jewels. HSMs, strict access controls, proper rotation schedules, full-chain and sensible life-span. The point about concentrated risk is bang on, you've turned thousands of distributed CA keys into one single target. So act like it. Run it like a proper CA with proper key signing ceremonies and all the safeguards etc.

Actually invest in proper cert distribution. Configuration management (Ansible/Salt/whatever), golden container base images with the CA bundle baked in, MDM for endpoints, cloud-init for VMs. If you can't reliably push a cert bundle to your entire estate, you've got bigger problems than TLS inspection.

Train people properly on what errors are expected vs "drop everything and call security". Document the exceptions. Make reporting easy. Actually investigate when someone raises a TLS error they don't recognise. For dev's, it needs to just work without them even thinking about it. Then they don't need to work around it, ever. If they need to, the system is busted.

Scope it ruthlessly. Not everything needs to go through the proxy. Developer workstations with proper EDR? Maybe exclude them. Production services with cert pinning? Route direct. Every blanket "intercept everything" policy I've seen has been a disaster. Particularly for end-users doing personal banking, medical stuff, therapy sessions, do you really want IT/Sec seeing that?

Use it alongside modern defences. ie EDR, Zero Trust, behavioural analytics, CASB. It should be one layer in defence-in-depth, not your entire security strategy.

Build observability, you need metrics on what's being inspected, what's bypassing, failure rates, performance impact. If you can't measure it, you can't manage it.

But Yeah, the core criticism stands though, even done well, it's a massive operational burden and it actively undermines trust in TLS. The failure modes are particularly insidious because you're training people to ignore the very warnings that are meant to protect them.

The real question isn't "TLS inspection: yes or no?" It's: "Do we have the organisational maturity, resources, and commitment to do this properly?" If you're not in a regulated industry or don't have dedicated security teams and mature infrastructure practices, just don't bother. But if you must do it, and plenty of organisations genuinely must, then do it properly or don't do it at all.

This is a massive pain at my work, same as I'm sure most other comments are saying.

I use Platform.IO for firmware development and can't build my firmware unless I hotspot my phone. I would say that's a PIO bug unless there is a flag I don't know about, but it's exposed by this nuisance of a firewall.

The devs where I am spend much of our time hotspotted to our phones with the corporate network never connected so IP goes out over the mobile network.

Whenever possible we use 'do not verify server certs' flags in libs and commands which is not ideal.

"If you use my (private) network you follow my rules"

And I find it hard to argue with that.

I've been using a VPN habitually on my phone and my (personal) laptop for a decade now. Work, home, travel. Doesn't matter. It's always on.

Got acquired by a Fortune 500 and recieved new laptop. First hour I'm seeing TLS errors everywhere except the browser. They'd half-baked their internal CA rollout, so wasn't trusted properly.

By day two I started validating their setup. The CA literally had a typo in the company name, not a great sign.

A quick check with badssl.com showed that any self-signed(!) cert was being transparently MITM'ed and re-signed by their trusted corporate cert. Took them 40 days to fix it.

Another fun side-effect of this is that devs will just turned off TLS verification, so their codebase is full of `curl -k`, `verify_mode = VERIFY_NONE`, `ServerCertificateValidationCallback = () => true`, ... Exactly the thing you want to see at a big fintech company /s

More and more big customers (especially banks) are requiring this kind of self-inflicted-MITM attack from all their suppliers. Do you want to have customers? Get ready for zscaler!

How do you propose compliance with their exfiltration protection requirements? (And “turn down $ from those customers” is not an answer)

I work for a school. My traffic is not MITM'd, but the kids' traffic is, because we don't want them using their school-issued laptops to play games or go shopping, and you can't adequately block stuff if it's all encrypted.

I'm glad someone is speaking out about this. When I first found out that the major Fortune 500 company I was working for did this, I was happy I never did any online banking or any personal finance logins using the work computer. It's obscene, quite frankly. I have many criticisms of big-corpo security and how overbearing and paranoid it has become such that developers can barely get a thing done in a lot of these big firms.

Plus, most of the internal threats are embezzlers who get away with it (for awhile, at least). I did work for one place that had a Chinese national attempt to make off with the entire customer database, but he did it by burning CDs (circa 2006).

I'd like to know if there is any real world data about the effectiveness of TLS inspection in preventing harm. It's empirically a massive tax on any organisation that engages in any kind of software engineering or technical work. I estimate that something like 3% of all our engineering effort goes to working around the TLS inspection which breaks security on literally every piece of infrastructure we build. And it embeds all the harm that the article alludes to (and more). So it takes quite a significant balance of upside to counteract that.

So is the benefit worth it? Is there data to prove it? Or is it just authoritarian IT departments drunk on power implementing this stuff?

I'd love to know.