Summary
Vyper's extract32 can ready dirty memory
When using the built-in extract32(b, start), if the start index provided has for side effect to update b, the byte array to extract 32 bytes from, it could be that some dirty memory is read and returned by extract32.
As of v0.4.0 (specifically, commit https://github.com/vyperlang/vyper/commit/3d9c537142fb99b2672f21e2057f5f202cde194f), the compiler will panic instead of generating bytecode.
Details
Before evaluating start, the function Extract32.build_IR caches only:
- The pointer in memory/storage to
b: https://github.com/vyperlang/vyper/blob/10564dcc37756f3d3684b7a91fd8f4325a38c4d8/vyper/builtins/functions.py#L916-L918 - The length of
b: https://github.com/vyperlang/vyper/blob/10564dcc37756f3d3684b7a91fd8f4325a38c4d8/vyper/builtins/functions.py#L920-L922
but do not cache the actual content of b. This means that if the evaluation of start changes b's content and length, an outdated length will be used with the new content when extracting 32 bytes from b.
PoC
Calling the function foo of the following contract returns b'uuuuuuuuuuuuuuuuuuuuuuuuuuu\x00\x00789' meaning that extract32 accessed some dirty memory.
var:Bytes[96]
@internal
def bar() -> uint256:
self.var = b'uuuuuuuuuuuuuuuuuuuuuuuuuuuuuu'
self.var = b''
return 3
@external
def foo() -> bytes32:
self.var = b'abcdefghijklmnopqrstuvwxyz123456789'
return extract32(self.var, self.bar(), output_type=bytes32)
# returns b'uuuuuuuuuuuuuuuuuuuuuuuuuuu\x00\x00789'
Impact
For contracts that are affected, it means that calling extract32 returns dirty memory bytes instead of some expected output.
A read operation accesses a memory location beyond the intended buffer boundary. Typical impact: sensitive data disclosure or crash.
CVE-2024-24564 has a CVSS score of 3.7 (Low). 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 (0.4.0); 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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Frequently Asked Questions
- What is CVE-2024-24564? CVE-2024-24564 is a low-severity out-of-bounds read vulnerability in vyper (pip), affecting versions <= 0.3.10. It is fixed in 0.4.0. A read operation accesses a memory location beyond the intended buffer boundary.
- How severe is CVE-2024-24564? CVE-2024-24564 has a CVSS score of 3.7 (Low). 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-2024-24564? vyper (pip) versions <= 0.3.10 is affected.
- Is there a fix for CVE-2024-24564? Yes. CVE-2024-24564 is fixed in 0.4.0. Upgrade to this version or later.
- Is CVE-2024-24564 exploitable, and should I be worried? Whether CVE-2024-24564 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-2024-24564 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-2024-24564? Upgrade
vyperto 0.4.0 or later.