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High

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

  • Disclosed: 11.05.2023
  • Updated: 11.10.2026 15:17

Impact

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:

vyper
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:

vyper
@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:

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

Patches

patched in 4f8289a81206f767df1900ac48f485d90fc87edb

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?

Affected software

Click a technology to see all vulnerabilities affecting it.

PlatformPackageVulnerable versionsFixed in
Python (PyPI) vyper < 0.3.8 0.3.8

References

CVSS score 7.5/10
CVSS vector
CVSS:3.1/AV:N/AC:L/PR:N/UI:N/S:U/C:N/I:H/A:N
Weakness (CWE)
CWE-787
Platform
Python (PyPI)
Package
vyper
Disclosed
11.05.2023
Updated
11.10.2026 15:17

Sources and licenses

OSV / GitHub Advisory Database - PYSEC-2023-77 - PyPA Advisory Database; CC BY 4.0

OSV / GitHub Advisory Database - GHSA-3p37-3636-q8wv - CC BY 4.0

Vulnerability history: vyper

All published vulnerabilities of this package (Python (PyPI)), newest first. Shows whether this is a one-off slip or a package that needs watching.

All (47) in the archive
Total entries
47
First → latest
03.2020 10.2026
Without a fix
5
Exploited in attacks
0

Severity breakdown

  • Critical 3
  • High 14
  • Medium 20
  • Low 10

Disclosures per year

Severity:
  1. Vyper negative array index bounds checks
    Critical · 9.8 CVE-2024-24563 < 0.4.0 0.4.0
  2. Vyper's bounds check on built-in `slice()` function can be overflowed
    Critical · 9.8 CVE-2024-24561 < 0.4.0 0.4.0
  3. concat built-in can corrupt memory in vyper
    High · 7.3 CVE-2024-22419 >= 0.3.0, < 0.4.0 0.4.0
  4. incorrect storage layout for contracts containing large arrays
    High · 7.5 CVE-2023-46247 < 0.3.8 0.3.8
  5. Vyper vulnerable to memory corruption in certain builtins utilizing `msize`
    High · 8.1 CVE-2023-42443 >= 0.3.4, < 0.3.10 0.3.10
  6. Vyper has incorrectly allocated named re-entrancy locks
    Critical · 8.7 CVE-2023-39363 >= 0.2.15, < 0.3.1 0.3.1
  7. Vyper vulnerable to incorrect ordering of arguments for kwargs passed to internal calls
    High · 7.5 CVE-2023-32059 < 0.3.8 0.3.8
  8. Vyper vulnerable to integer overflow in loop
    High · 7.5 CVE-2023-32058 < 0.3.8 0.3.8
  9. Vyper vulnerable to OOB DynArray access when array is on both LHS and RHS of an assignment this entry
    High · 7.5 CVE-2023-31146 < 0.3.8 0.3.8
  10. vyper vulnerable to storage allocator overflow
    High · 7.5 CVE-2023-30837 < 0.3.8 0.3.8
  11. Incorrect success value returned in vyper
    High · 7.5 CVE-2023-30629 >= 0.3.1, < 0.3.8 0.3.8
  12. Multiple evaluation of contract address in call in vyper
    High · 7.5 CVE-2022-29255 < 0.3.4 0.3.4
  13. Vyper is a pythonic Smart Contract Language for the ethereum virtual machine. In affected versions, the return of `<iface>.returns_int128()` is not validated to fall within the bounds of `int128`. Thi
    High · 8.8 CVE-2022-24845 < 0.3.2 0.3.2
  14. Buffer Overflow in vyper
    High · 7.1 CVE-2022-24788 < 0.3.2 0.3.2
  15. Incorrect Comparison in Vyper
    High · 7.5 CVE-2022-24787 < 0.3.2 0.3.2
  16. Memory corruption when returning a literal struct with a private call inside of it
    High · 7.5 CVE-2021-41121 < 0.3.0 0.3.0
  17. Storage corruption due to variables overwritten by re-entrancy locks
    High ghsa-7f92-rr6w-cq64 >= 0.2.13, < 0.2.15 0.2.15

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