# CVE-2026-62381: luci-lib-px5g 2040-bit Certificate Signing Heap Buffer Overflow

> Heap buffer overflow in OpenWrt LuCI certificate signing allows potential code execution or denial of service via crafted RSA keys.

- **Severity:** Medium 6.9 (`CVSS:4.0/AV:L/AC:L/AT:N/PR:L/UI:N/VC:L/VI:L/VA:H/SC:N/SI:N/SA:N`)
- **Exploited in the wild:** Not known
- **Login needed:** Any signed-in user
- **Attackable:** Local or same network only
- **Victim action needed:** Not needed
- **Fix available:** No
- **Published:** 22 Aug 2026
- **Updated:** 24 Aug 2026
- **Also known as:** GHSA-g4fj-xr23-w9hm, GHSA-jgc3-4q3p-g6xh

## What is CVE-2026-62381?

CVE-2026-62381 is a medium-severity memory corruption vulnerability in openwrt luci, published on 22 Aug 2026. It can only be exploited from the same machine or local network, with no action from the victim.

### Official description

luci-lib-px5g (LuCI) contains a heap-based buffer overflow in the native ASN.1 encoding routine asn1_add_obj (x509write.c) when signing a certificate with a 2040-bit RSA key. For a 255-byte signature, the BIT STRING allocation is computed from the DER length encoding of 255 bytes, but the payload written after prepending the unused-bits byte is 256 bytes, requiring one additional DER length octet. As a result the allocation is 259 bytes while the tag, length, unused-bits byte, and signature require 260 bytes, and the final memcpy writes one byte beyond the heap buffer. The overflow is reachable through the exported Lua interface via create_selfsigned(); whether it is remotely exploitable depends on the embedding application. The vulnerable code is present on the openwrt-18.06 through openwrt-25.12 release branches and is absent from master, where the luci-lib-px5g package has been removed rather than patched.

Weakness: CWE-122 (Heap-based Buffer Overflow)

## Which versions are affected by CVE-2026-62381?


## How do I fix CVE-2026-62381?

No fix has been published for CVE-2026-62381 yet. Limit exposure of the affected software until one is available.

## Is CVE-2026-62381 being exploited?

It is not confirmed as exploited in the wild, but public exploit code for CVE-2026-62381 exists.

## Fix prompt for AI coding agents

```text
Check this codebase for CVE-2026-62381 and fix it if it is affected.

What it is: CVE-2026-62381 is a medium-severity memory corruption vulnerability in openwrt luci, published on 22 Aug 2026. It can only be exploited from the same machine or local network, with no action from the victim.
Exploitation: It is not confirmed as exploited in the wild, but public exploit code for CVE-2026-62381 exists.

Affected product: openwrt luci. No package-level version data is available, so check the vendor advisory linked from the reference page.

Task:
1. Search the dependency manifests and lockfiles (for example package.json, package-lock.json, requirements.txt, poetry.lock, uv.lock, pom.xml, build.gradle, go.mod, Cargo.lock, Gemfile.lock) and any Dockerfiles for the affected packages, including transitive dependencies.
2. If an affected version is in use, upgrade it to the fixed version for its release line with the project's package manager, so the lockfile is regenerated. Prefer the smallest upgrade that fixes it.
3. If there is no fix, or the upgrade would break the build, do not guess: explain the risk and the safest workaround instead.
4. Run the tests and summarise what changed and why.
5. If nothing in the project is affected, say so and change nothing.

Reference: https://insights.sbomify.com/CVE-2026-62381/ (Markdown: https://insights.sbomify.com/CVE-2026-62381/index.md)
```

## Sources

- CVE record: https://www.cve.org/CVERecord?id=CVE-2026-62381
- NVD: https://nvd.nist.gov/vuln/detail/CVE-2026-62381
- OSV: https://osv.dev/vulnerability/CVE-2026-62381

---
From sbomify Insights: https://insights.sbomify.com/CVE-2026-62381/
Summaries are generated and may contain mistakes; the official description above is the record.