CVE-2023-31146

Vyper vulnerable to OOB DynArray access when array is on both LHS and RHS of an assignment

Workarounds

Is there a way for users to fix or remediate the vulnerability without upgrading?

References

Are there any links users can visit to find out more?

during codegen, the length word of a dynarray is written before the data, which can result in OOB array access in the case where the dynarray is on both the lhs and rhs of an assignment. here is a minimal example producing the issue:

a:DynArray[uint256,3]
@external
def test() -> DynArray[uint256,3]:
    self.a = [1,2,3]
    self.a = empty(DynArray[uint256,3])
    self.a = [self.a[0],self.a[1],self.a[2]]
    return self.a # return [1,2,3]

and here is an example demonstrating the issue can cause data corruption across call frames:

@external
def test() -> DynArray[uint256,3]:
    self.a()
    return self.b() # return [1,2,3]

@internal
def a():
    a: uint256 = 0    
    b: uint256 = 1    
    c: uint256 = 2    
    d: uint256 = 3

@internal
def b() -> DynArray[uint256,3]:
    a: DynArray[uint256,3] = empty(DynArray[uint256,3])
    a = [a[0],a[1],a[2]]
    return a

examples involving append and pop:

@internal
def foo():
    c: DynArray[uint256, 1] = []
    c.append(c[0])

@internal
def foo():
    c: DynArray[uint256, 1] = [1]
    c[0] = c.pop()

the expected behavior in all of the above cases is to revert due to oob array access.

A write operation targets a memory location beyond the intended buffer boundary. Typical impact: memory corruption, crash, or arbitrary code execution.

CVE-2023-31146 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.

Kodem intelligence

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patched in 4f8289a81206f767df1900ac48f485d90fc87edb

1. What is CVE-2023-31146? CVE-2023-31146 is a high-severity out-of-bounds write vulnerability in vyper (pip), affecting versions < 0.3.8. It is fixed in 0.3.8. A write operation targets a memory location beyond the intended buffer boundary.
2. How severe is CVE-2023-31146? CVE-2023-31146 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.
3. Which versions of vyper are affected by CVE-2023-31146? vyper (pip) versions < 0.3.8 is affected.
4. Is there a fix for CVE-2023-31146? Yes. CVE-2023-31146 is fixed in 0.3.8. Upgrade to this version or later.
5. Is CVE-2023-31146 exploitable, and should I be worried? Whether CVE-2023-31146 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
6. What actually determines whether CVE-2023-31146 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.
7. How do I fix CVE-2023-31146? Upgrade vyper to 0.3.8 or later.

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