How severe is GHSA-4w26-8p97-f4jp?

No CVSS score has been assigned to GHSA-4w26-8p97-f4jp yet. Review the advisory details and affected package list to assess your exposure.

Which packages are affected by GHSA-4w26-8p97-f4jp?

GHSA-4w26-8p97-f4jp affects the following packages: vyper (PyPI). Ecosystems affected: PyPI.

How do I fix GHSA-4w26-8p97-f4jp?

Update vyper to 0.4.1 or later, then make sure no transitive (indirect) dependency still pins the vulnerable range — O3 confirms GHSA-4w26-8p97-f4jp is resolved across your whole dependency graph.

How do I detect GHSA-4w26-8p97-f4jp in my PyPI dependencies?

Scan your dependency tree (package-lock.json, pnpm-lock.yaml, requirements.txt, go.sum, etc.) for vyper, including transitive dependencies — a direct dependency you never call can still pull in a vulnerable version.

How do I mitigate GHSA-4w26-8p97-f4jp if there is no patch (or I can't update yet)?

Stop feeding it untrusted input: reject or quarantine files and payloads from unverified sources until you can upgrade, restrict accepted formats to the ones you actually need, and run the parsing or decoding step in a least-privileged sandbox or short-lived worker so a crash or corrupted read cannot reach the rest of the process.

Is GHSA-4w26-8p97-f4jp actively exploited in the wild?

No public exploit code has been indexed for GHSA-4w26-8p97-f4jp yet. This does not mean the vulnerability cannot be exploited — absence of public exploits does not imply safety. Apply the recommended fix and use O3 Security to monitor your exposure.

What is the EPSS score for GHSA-4w26-8p97-f4jp?

GHSA-4w26-8p97-f4jp has an EPSS (Exploit Prediction Scoring System) score of 0.6%, placing it in the 47th percentile of all CVEs. EPSS is maintained by FIRST.org and estimates the probability that a vulnerability will be exploited in the wild within the next 30 days. This score indicates relatively lower exploitation probability, though the CVSS severity should still guide your patching priority.

What type of vulnerability is GHSA-4w26-8p97-f4jp?

GHSA-4w26-8p97-f4jp is classified as Out-of-bounds Write (CWE-787). This weakness type describe the underlying flaw category, which helps determine the potential impact and the right class of mitigation.

When was GHSA-4w26-8p97-f4jp published, and has it been updated?

GHSA-4w26-8p97-f4jp was published on February 21, 2025 and was last updated on April 9, 2025. Advisory data evolves as severity scores, affected ranges, and exploit intelligence are revised — always check the latest version of the advisory before acting.

AugAssign evaluation order causing OOB write within the…

Exploitation Status

No confirmed exploitation observed yet

CISA assesses this as automatable — exploitation doesn’t require manual, per-target effort, which raises the odds of mass scanning and opportunistic attacks.
CISA’s own triage has not observed active exploitation or public proof-of-concept code for this CVE as of its last assessment.

Exploitation and automatability from CISA’s SSVC triage for GHSA-4w26-8p97-f4jp.

EPSS Exploitation Probability

via FIRST.org ↗

0.6%probability of exploitation in next 30 days

Lower Risk0.00%

Lower risk than most CVEs47th percentile — riskier than 47% of all scored CVEsHighest risk

Probability of exploitation in the next 30 days, from FIRST.org EPSS.

Real-World Exposure

1 pkg affected

🐍vyper

Real-time download stats are indexed for npm and PyPI packages. This vulnerability affects PyPI packages — download data is not available via public APIs for these ecosystems.

Description

Vyper handles AugAssign statements by first caching the target location to avoid double evaluation. However, in the case when target is an access to a DynArray and the rhs modifies the array, the cached target will evaluate first, and the bounds check will not be re-evaluated during the write portion of the statement. In other words, the following code

def poc():
    a: DynArray[uint256, 2] = [1, 2]
    a[1] += a.pop()

is equivalent to:

def poc():
    a: DynArray[uint256, 2] = [1, 2]
    a[1] += a[len(a) - 1]
    a.pop()

rather than:

def poc():
    a: DynArray[uint256, 2] = [1, 2]
    s: uint256 = a[1]
    t: uint256 = a.pop()
    a[1] = s + t  # reverts due to oob access

Affected Packages

1 total 1 fixed

Ecosystem	Package	Vulnerable range	Fix
🐍PyPI	`vyper`	all versions	0.4.1`pip install --upgrade 'vyper==0.4.1'`

Affected Products

1 product · 1 configurations

Application

vypervyperlang

< 0.4.1

range

Detection & mitigation playbook

Open-source dependency

Detect
Scan your dependency tree (package-lock.json, pnpm-lock.yaml, requirements.txt, go.sum, etc.) for vyper, including transitive dependencies — a direct dependency you never call can still pull in a vulnerable version.
Fix
Update vyper to 0.4.1 or later, then make sure no transitive (indirect) dependency still pins the vulnerable range — O3 confirms GHSA-4w26-8p97-f4jp is resolved across your whole dependency graph.
Workarounds
Stop feeding it untrusted input: reject or quarantine files and payloads from unverified sources until you can upgrade, restrict accepted formats to the ones you actually need, and run the parsing or decoding step in a least-privileged sandbox or short-lived worker so a crash or corrupted read cannot reach the rest of the process.

Frequently Asked Questions

Vyper handles AugAssign statements by first caching the target location to avoid double evaluation. However, in the case when target is an access to a DynArray and the rhs modifies the array, the cached target will evaluate first, and the bounds check will not be re-evaluated during the write portion of the statement. In other words, the following code ```vyper def poc(): a: DynArray[uint256, 2] = [1, 2] a[1] += a.pop() ``` is equivalent to: ```vyper def poc(): a: DynArray[uint256, 2] = [1, 2] a[1] += a[len(a) - 1] a.pop() ``` rather than: ```vyper def poc(): a: DynAr

O3 Security · Impact-Aware SCA

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AugAssign evaluation order causing OOB write within the object in VyperGHSA-4w26-8p97-f4jp