GHSA-9rcw-c2f9-2j55
NONEOpenZeppelin Contracts Bytes's lastIndexOf function with position argument performs out-of-bound memory access on empty buffers
EPSS Exploitation Probability
EPSS (Exploit Prediction Scoring System) is a daily probability model maintained by FIRST.org. It estimates the likelihood a CVE will be exploited in production environments within the next 30 days, derived from real-world threat intelligence signals.
Blast Radius
Weekly download volume for affected packages — a proxy for how broadly this vulnerability is deployed.
@openzeppelin/contractsnpm@openzeppelin/contracts-upgradeablenpmDescription
Impact
The lastIndexOf(bytes,byte,uint256) function of the Bytes.sol library may access uninitialized memory when the following two conditions hold: 1) the provided buffer length is empty (i.e. buffer.length == 0) and position is not 2**256 - 1 (i.e. pos != type(uint256).max).
The pos argument could be used to access arbitrary data outside of the buffer bounds. This could lead to the operation running out of gas, or returning an invalid index (outside of the empty buffer). Processing this invalid result for accessing the buffer would cause a revert under normal conditions.
When triggered, the function reads memory at offset buffer + 0x20 + pos. If memory at that location (outside the buffer) matches the search pattern, the function would return an out of bound index instead of the expected type(uint256).max. This creates unexpected behavior where callers receive a valid-looking index pointing outside buffer bounds.
Subsequent memory accesses that don't check bounds and use the returned index must carefully review the potential impact depending on their setup. Code relying on this function returning type(uint256).max for empty buffers or using the returned index without bounds checking could exhibit undefined behavior.
Patches
Upgrade to 5.4.0
Affected Packages
| Ecosystem | Package | Vulnerable range | Fix |
|---|---|---|---|
| 📦npm | @openzeppelin/contracts | ≥ 5.2.0&&< 5.4.0 | 5.4.0 |
| 📦npm | @openzeppelin/contracts-upgradeable | ≥ 5.2.0&&< 5.4.0 | 5.4.0 |
Detection & mitigation playbook
Open-source dependencyDetect
Scan your dependency tree (package-lock.json, pnpm-lock.yaml, requirements.txt, go.sum, etc.) for @openzeppelin/contracts. O3's reachability analysis confirms whether the vulnerable code path is actually invoked in your application, so you act on real exposure instead of every transitive match.
Fix
Update @openzeppelin/contracts to 5.4.0 or later, then make sure no transitive (indirect) dependency still pins the vulnerable range — O3 confirms GHSA-9rcw-c2f9-2j55 is resolved across your whole dependency graph.
Workarounds
If you can't upgrade right away: gate or disable the affected feature, validate untrusted input at the boundary, and avoid passing attacker-controlled data into the vulnerable path. O3's runtime protection blocks exploitation in production as an interim safeguard until the upgrade lands.
How O3 protects you
O3 pinpoints whether GHSA-9rcw-c2f9-2j55 is reachable in your code and exactly where to fix it, then blocks exploitation in production at runtime until the patched version is deployed.
Tailored to GHSA-9rcw-c2f9-2j55. Runtime protection reduces exposure until a permanent patch is applied and verified — it complements patching, it doesn't replace it.
Frequently Asked Questions
Is GHSA-9rcw-c2f9-2j55 in your dependencies?
O3 detects GHSA-9rcw-c2f9-2j55 across npm dependencies and uses function-level reachability to confirm whether the vulnerable code path is actually reachable — not just present. No false positives.