Summary
Incorrect success value returned in vyper
Background
During the audit of Lido's Gate Seals code statemind team identified a weird behavior of the code that uses raw_call: https://github.com/lidofinance/gate-seals/blob/051593e74df01a4131c485b4fda52e691cd4b7d8/contracts/GateSeal.vy#L164 .
Construction like this:
success = raw_call(
sealable,
_abi_encode(SEAL_DURATION_SECONDS, method_id=method_id("pauseFor(uint256)")),
revert_on_failure=False
)
was not fully documented: https://docs.vyperlang.org/en/v0.3.7/built-in-functions.html#raw_call .
The documentation says that: if max_outsize=0 it should return nothing and then it says that if revert_on_failure=False it should return a success flag in the tuple of response, but what if max_outsize=0 and revert_on_failure=False.
So the team started researching what exactly happened in that case, after some research we found that the Vyper compiler generates the wrong bytecode in that case, it generates the sequence:
CALL // call
MLOAD // MLOAD is wrong since the CALL result is already stored in the stack
Workarounds
The simple workaround is always to put max_outsize>0.
Workaround example https://github.com/lidofinance/gate-seals/pull/5/files
References
Lido's fix: https://github.com/lidofinance/gate-seals/pull/5/files
Impact
Example of buggy code:
@external
def returnSome(calling: address, a: uint256) -> bool:
success: bool = false
success = raw_call(
calling,
_abi_encode(a, method_id=method_id("a(uint256)")),
revert_on_failure=False
)
any contract that uses the raw_call with revert_on_failure=False and max_outsize=0 receives the wrong response from raw_call. Depending on the memory garbage, the result can be either True or False.
CVE-2023-30629 has a CVSS score of 7.5 (High). The vector is network-reachable, no privileges required, and no user interaction. A CVSS score reflects the worst-case severity of the vulnerability, not your specific exposure. Whether this affects your application depends on whether the vulnerable code is present and reachable in your environment. A fixed version is available (0.3.8); upgrading removes the vulnerable code path.
Affected versions
Security releases
Kodem intelligence
Severity tells you how bad this could be in the worst case. It does not tell you whether you are exposed. Exploitability and impact are functions of runtime truth: whether the vulnerable code is present, reachable, and actually executes in your application. A vulnerable package can sit in your dependency tree and never run.
Kodem, an Intelligent Application Security platform, uses runtime intelligence to reveal which vulnerabilities actually execute in production, so teams prioritize the ones that genuinely matter. Kodem's runtime-powered SCA identifies whether this CVE is reachable in your applications.
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Fix by @charles-cooper https://github.com/vyperlang/vyper/commit/851f7a1b3aa2a36fd041e3d0ed38f9355a58c8ae
Frequently Asked Questions
- What is CVE-2023-30629? CVE-2023-30629 is a high-severity security vulnerability in vyper (pip), affecting versions >= 0.3.1, < 0.3.8. It is fixed in 0.3.8.
- How severe is CVE-2023-30629? CVE-2023-30629 has a CVSS score of 7.5 (High). This score reflects the worst-case severity of the vulnerability, not your specific exposure. Whether it represents real risk in your environment depends on whether the vulnerable code is present and reachable.
- Which versions of vyper are affected by CVE-2023-30629? vyper (pip) versions >= 0.3.1, < 0.3.8 is affected.
- Is there a fix for CVE-2023-30629? Yes. CVE-2023-30629 is fixed in 0.3.8. Upgrade to this version or later.
- Is CVE-2023-30629 exploitable, and should I be worried? Whether CVE-2023-30629 is exploitable in your environment depends on whether the vulnerable code is present and reachable. A CVSS score is a worst-case rating; it does not account for your specific deployment, configuration, or usage patterns. Kodem, an Intelligent Application Security platform, uses runtime intelligence to show which vulnerabilities actually execute in production, so you can focus on the ones that represent real risk. Get a demo
- What actually determines whether CVE-2023-30629 is exploitable, and how bad it is? Exploitability and impact are not fixed properties of a CVE. They depend on runtime truth: whether the vulnerable code is present, reachable, and actually executes in your application. A high CVSS score on a dependency that never runs is not the same as real risk. Kodem, an Intelligent Application Security platform, uses runtime intelligence to reveal which vulnerabilities actually execute in production, so teams prioritize the ones that genuinely matter.
- How do I fix CVE-2023-30629? Upgrade
vyperto 0.3.8 or later.