---
id: CVE-2026-62381
title: >-
  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
summary: >-
  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
  compute…
severity: medium
cvss: 6.6
cvssVector: 'CVSS:3.1/AV:L/AC:L/PR:L/UI:N/S:U/C:L/I:L/A:H'
cwe:
  - CWE-122
published: '2026-08-22'
updated: '2026-09-24'
sourceUpdated: '2026-09-24T20:43:32.537'
source: NVD
sourceUrl: 'https://nvd.nist.gov/vuln/detail/CVE-2026-62381'
references:
  - url: 'https://github.com/openwrt/luci/security/advisories/GHSA-jgc3-4q3p-g6xh'
    label: disclosure@vulncheck.com
  - url: >-
      https://www.vulncheck.com/advisories/luci-lib-px5g-2040-bit-certificate-signing-heap-buffer-overflow
    label: disclosure@vulncheck.com
  - url: 'https://github.com/openwrt/luci/security/advisories/GHSA-jgc3-4q3p-g6xh'
    label: 134c704f-9b21-4f2e-91b3-4a467353bcc0
tags:
  - nvd
epss: 0.00102
epssPercentile: 0.00867
ingestedAt: '2026-08-23T04:42:14.698Z'
---

## Overview

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.

## Remediation

Refer to the linked advisories for vendor-supplied fixes and affected version ranges.