How we exploited CodeRabbit: From simple PR to RCE and write access on 1M repos
77 comments
·August 19, 2025ketzo
> While running the exploit, CodeRabbit would still review our pull request and post a comment on the GitHub PR saying that it detected a critical security risk, yet the application would happily execute our code because it wouldn’t understand that this was actually running on their production system.
What a bizarre world we're living in, where computers can talk about how they're being hacked while it's happening.
Also, this is pretty worrisome:
> Being quick to respond and remediate, as the CodeRabbit team was, is a critical part of addressing vulnerabilities in modern, fast-moving environments. Other vendors we contacted never responded at all, and their products are still vulnerable. [emphasis mine]
Props to the CodeRabbit team, and, uh, watch yourself out there otherwise!
progforlyfe
Beautiful that CodeRabbit reviewed an exploit on its own system!
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chanon
Oh my god. I haven't finished reading that yet, it became too much to comprehend. Too stressful to take in the scope. The part where he could have put malware into release files of 10s of thousands (or millions?) of open source tools/libraries/software. That could have been a worldwide catastrophe. And who knows what other similar vulnerabilities might still exist elsewhere.
chanon
I'm starting to think these 'Github Apps' are a bad idea. Even if CodeRabbit didn't have this vulnerability, what guarantee do we have that they will always be good actors? That their internal security measures will ensure that none of their employees may do any malicious things?
Taking care of private user data in a typical SaaS is one thing, but here you have the keys to make targetted supply chain attacks that could really wreak havoc.
gz09
Correct me if I'm wrong, but the problem here is not with GitHub Apps, instead CodeRabbit violated the principle of least privilege: ideally the private key of their app should never end up in the environment of a job for a client but rather a short lived token should be minted from it (for just a single repo (for which the job is running)) so it never gets anywhere near those areas where one of their clients has any influence over what runs.
filleokus
I agree, this seems like straight up bad design from a security perspective.
But at the same time, me as the customer of Github, would prefer if Github made it harder for vendors like CodeRabbit to make misstakes like this.
If you have an app with access to more than 1M repos, it would make sense for Github to require a short lived token to access a given repository and only allow the "master" private key to update the app info or whatever.
And/or maybe design mechanisms that only allow minting of these tokens for the repo whenever a certain action is run (i.e not arbitrarily).
But at the end of the day, yes, it's impossible for Github to both allow users to grant full access to whatever app and at the same time ensure stuff like this doesn't happen.
risyachka
Software industry really needs at least some guardrails/regulations at this point.
It is absurd that anyone can mess up anything and have absolutely 0 consequences.
thyrfa
It is incredibly bad practice that their "become the github app as you desire" keys to the kingdom private key was just sitting in the environment variables. Anybody can get hacked, but that's just basic secrets management, that doesn't have to be there. Github LITERALLY SAYS on their doc that storing it in an environment variable is a bad idea. Just day 1 stuff. https://docs.github.com/en/apps/creating-github-apps/authent...
doesnt_know
If it’s not a secret that is used to sign something, then the secret has to get from the vault to the application at some point.
What mechanism are you suggesting where access to the production system doesn’t let you also access that secret?
Like I get in this specific case where you are running some untrusted code, that environment should have been isolated and these keys not passed in, but running untrusted code isn’t usually a common feature of most applications.
Nextgrid
If you actually have a business case for defense in depth (hint: nobody does - data breaches aren't actually an issue besides temporarily pissing off some nerds, as Equifax' and various companies stock prices demonstrate), what you'd do is have a proxy service who is entrusted with those keys and can do the operations on behalf of downstream services. It can be as simple as an HTTP proxy that just slaps the "Authorization" header on the requests (and ideally whitelists the URL so someone can't point it to https://httpbin.org/get and get the secret token echoed back).
This would make it so that even a compromised downstream service wouldn't actually be able to exfiltrate the authentication token, and all its misdeeds would be logged by the proxy service, making post-incident remediation easier (and being able to definitely prove whether anything bad has actually happened).
curuinor
hey, this is Howon from CodeRabbit. We use a cloud-provider-provided key vault for application secrets, including GH private key.
ipython
This reply, while useful, only serves to obfuscate and doesn’t actually answer the question.
You can store the credentials in a key vault but then post them on pastebin. The issue is that the individual runner has the key in its environment variables. Both can be true- the key can be given to the runner in env and the key is stored in a key vault.
The important distinction here is - have you removed the master key and other sensitive credentials from the environment passed into scanners that come in contact with customer untrusted code??
thyrfa
Not at that time though, right, considering it was dumped? You have changed since, which is good, but under a year ago had it as just an env var
iTokio
That’s why I’m worried about the growing centralization of things such as Chrome, Gmail, AWS, Cloudflare…
It’s very efficient to delegate something to one major actor but we are introducing single points of failure and are less resilient to vulnerabilities.
Critical systems should have defenses in depth, decentralized architectures and avoid trusting new providers with too many moving parts.
curuinor
hey, this is Howon from CodeRabbit here. we wish to note that this RCE was reported and fixed in January. it was entirely prospective and no customer data was affected. we have extensive sandboxing for basically any execution of anything now, including any and every tool and all generated code of any kind under the CodeRabbit umbrella.
if you want to learn how CodeRabbit does the isolation, here's a blog post about how: https://cloud.google.com/blog/products/ai-machine-learning/h...
mpeg
Where can we find the blog post you made back in January about the RCE fix explaining what measures you took to check if any customer data had been affected?
frankfrank13
Reading this, its not clear how your blog posts relates:
1. You run git clone inside the GCR function, so, you have at the very least a user token for the git provider
2. RCE exploit basically used the external tools, like a static analysis checker, which again, is inside your GCR function
3. As a contrived example, if I could RCE `console.log(process.env)` then seemingly I could do `fetch(mywebsite....`
I get it, you can hand wave some amount of "VPC" and "sandbox" here. But, you're still executing code, explicitly labeling it "untrusted" and "sandboxed" doesn't excuse it.
thyrfa
How can you guarantee that nobody ripped the private key before the researcher told you about the issue though?
KingOfCoders
Or has a backdoor installed somewhere?
cleverwebb
how do you know that no customer data was affected? did you work with github and scan all uses of your keys? how do you know if a use of your github key was authentic or not? did you check with anthroipic/openai/etc to scan logs usage?
It's really hard to trust a "hey we got this guys" statement after a fuckup this big
Xunjin
That's why countries should start to legislate on these matters, there are no incentives in focusing on security and properly report to the customers such vulnerability.
elpakal
> Sandboxing: All Cloud Run instances are sandboxed with two layers of sandboxing and can be configured to have minimal IAM permissions via dedicated service identity. In addition, CodeRabbit is leveraging Cloud Run's second generation execution environment, a microVM providing full Linux cgroup functionality. Within each Cloud Run instance, CodeRabbit uses Jailkit to create isolated processes and cgroups to further restrict the privileges of the jailed process.
In case you don't want to read through the PR
tadfisher
But do you still store your GH API private key in environment variables?
curuinor
hey, this is Howon from CodeRabbit. We use a cloud-provider-provided key vault for application secrets, including GH private key.
yunohn
While I fully understand that things sometimes get missed, it just seems really bizarre to me that somehow “sandboxing/isolation” was never considered prior to this incident. To me, it feels like the first thing to implement in a system that is explicitly built to run third party untrusted code?
wging
The article seems to imply that something of the sort had actually been attempted prior to the incident, but was either incomplete or buggy. I'm not sure the details would be entirely exculpatory, but unless you want to flatly disbelieve their statements, "not considered" isn't quite right.
> After responsibly disclosing this critical vulnerability to the CodeRabbit team, we learned from them that they had an isolation mechanism in place, but Rubocop somehow was not running inside it.
elpakal
> After responsibly disclosing this critical vulnerability to the CodeRabbit team, we learned from them that they had an isolation mechanism in place, but Rubocop somehow was not running inside it.
Curious what this (isolation mechanism) means if anyone knows.
benmmurphy
What a lucky coincidence that the tool the researcher attacked because it allowed code execution was not sandboxed.
diggan
> Curious what this (isolation mechanism) means if anyone knows.
If they're anything like the typical web-startup "developing fast but failing faster", they probably are using docker containers for "security isolation".
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kachapopopow
you could say that they have vibe forgotten to sandbox it.
(likely asked AI to implement x and ai completely disregarded the need to sandbox).
brainless
I did not understand something: why did CodeRabbit run external tools on external code within its own set of environment variables? Why are these variables needed for this entire tooling?
tadfisher
> Why are these variables needed for this entire tooling?
They are not. The Github API secret key should never be exposed in the environment, period; you're supposed to keep the key in an HSM and only use it to sign the per-repo access token. Per the GH docs [0]:
> The private key is the single most valuable secret for a GitHub App. Consider storing the key in a key vault, such as Azure Key Vault, and making it sign-only. This helps ensure that you can't lose the private key. Once the private key is uploaded to the key vault, it can never be read from there. It can only be used to sign things, and access to the private key is determined by your infrastructure rules.
> Alternatively, you can store the key as an environment variable. This is not as strong as storing the key in a key vault. If an attacker gains access to the environment, they can read the private key and gain persistent authentication as the GitHub App.
[0]: https://docs.github.com/en/apps/creating-github-apps/authent...
immibis
Environment variables used to be standard practice for API keys. It seems like every time someone finds a way to get a key, standard practice gets more convoluted.
gdbsjjdn
It sounds like they were putting these processes in a chroot jail or something and not allowing them to access the parent process env vars. There's a continuum of ways to isolate child processes in Linux that don't necessarily involve containers or docker.
The_Fox
Their own tools would need the various API keys, of course, and they did build a method to filter out those variables and managed most user code through it, but it sounds like they forgot to put Rubocop through the special method.
So this researcher may have gotten lucky in choosing to dig into the tool that CodeRabbit got unlucky in forgetting.
chuckadams
It sounds like a pretty bad approach in general to have to "filter out the bad stuff" on a case-by-case basis. It should be as simple as launching everything from a sanitized parent environment, and making it impossible to launch any tool otherwise. Or better, make that sanitized environment the default and make privileged operations be the thing that jumps through hoops to talk to a bastion/enclave/whatever that holds the actual keys.
The_Fox
Yes although somewhere there will be an `if` statement to determine if the process being started should get the complete environment or a key to get the other keys or whatever. Best to make that `if` at the highest level of the architecture as possible and wrapped in something that makes it obvious, like a `DangerousUserCodeProcess` class.
The only other safety I can think of is a whitelist, perhaps of file pathnames. This helps to maintain a safe-by-default posture. Taking it further, the whitelist could be specified in config and require change approval from a second team.
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elpakal
presuming they take the output of running these linters and pass it for interpretation to Claude or OpenAI
dpacmittal
I hope the author received a nice well deserved bounty for this find. Could have been catastrophic in the wrong hands.
cube00
When they're spinning it [1] as a PR opportunity with no mention of the breach there won't be a bounty.
hahn-kev
Why does CodeRabbit need write access to the git repo? Why doesn't Github let me limit it's access?
dpcx
Because it has the ability to write tests for the PR in question.
tadfisher
Then it should open a PR for those tests so it can go through the normal CI and review process.
tedivm
Doing that requires write access if you're a Github Application. You can't just fork repositories back into another org, since Github Applications only have the permissions of the single organization that they work with. Rulesets that prevent direct pushes to specific branches can help here, but have to be configured for each organization.
dpcx
It updates the existing PR with the tests, I believe. They'd still get reviewed and go through CI.
flippyhead
It's more than that. If can suggest fixes which you can directly commit.
edm0nd
No bounty was paid for this?
cube00
I can't say I'm surprised they didn't pay a bounty when they couldn't even own up to this on their own blog [1].
Instead they took it as an opportunity to market their new sandboxing on Google's blog [2] again with no mention of why their hand was forced into building the sandboxing they should have had before they rushed to onboard a million customers.
I have no idea what their plan was. They had to have known the researchers would eventually publish this. Perhaps they were hoping it wouldn't get the same amount of attention it would if they posted it on their own blog.
mpeg
First thing I looked for... this is an absolutely critical vulnerability that if exploited would have completely ruined their business. No bounty!?
vntok
Why would they pay anything? The researchers offered them the vuln analysis for free, unprompted.
If anything, they got paid in exposure.
cube00
Let's hope the grants keep coming in because those researchers will start getting offers from the darker corners of the web if bounties aren't paid.
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eranation
This is very similar to a CVE I discovered in cdxgen (CVE-2024-50611), which is similar to another CVE in Snyk's plugin (CVE-2022-24441). tl;dr if you run a scanner on untrusted code, ensure it doesn't have a way of executing that code.
Some ways to prevent this from happening:
1. Don't let spawned processes have access to your env, there are ways to allowlist a set of env vars that are needed for a sub process in all major languages
2. Don't store secrets in env vars, use a good secrets vault (with a cache)
3. Tenant isolation as much as you can
4. And most obviously - don't run processes that can execute the code they are scanning, especially if that code is not your code (harder to tell, but always be paranoid)
I think that Security fuckups of this disastrous scale should get classified as "breaches" or "incidents" and be required to be publicly disclosed by the news media, in order to protect consumers.
Here is a tool with 1 million customers which was breached with an exploit a clever 11 year old could created.
When the exploit is so simple, I find it likely that bots or Black Hats or APTs had already found a way in and established persistence before the White Hat researchers reported the issue. If this is the case, patching the issue might prevent NEW bad actors from penetrating CodeRabbit's environment, but it might not evict any bad actors which might now be lurking in their environment.
I know Security is hard, but come on guys