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

Quick assessment

Affected
openwrt luci
Exploitation
No confirmed in-the-wild exploitation; assess based on exposure
Recommended action
Check the vendor advisory and references for a fixed version. If immediate upgrade is impossible, restrict exposure and increase monitoring.

luci-lib-px5g（LuCI）组件中存在一个基于堆的缓冲区溢出漏洞，该漏洞位于原生 ASN.1 编码例程 （位于文件 x509write.c 中），在使用 2040 位 RSA 密钥签署证书时触发。对于长度为 255 字节的签名，BIT STRING 的分配大小是根据 DER 长度编码计算得出的，但在添加“未使用位数”字节并写入有效载荷后，实际数据大小为 256 字节，因此需要额外增加一个 DER 长度字节。结果是分配的堆缓冲区大小为 259 字节，而标签、长度、未使用位数字节和签名本身总共需要 260 字

CVSS 6.6 · Medium EPSS 0.10% · P1

Possible ATT&CK Techniques 1 AI

T1190 · Exploit Public-Facing Application

Affected Version Matrix 1

VendorProduct Version RangeStatus
openwrt luci ≤ 42d72f79cd8f057f241595abc761b39dab2d9f07 affected
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I. Basic Information for CVE-2026-62381

Vulnerability Information
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Vulnerability Title
luci-lib-px5g 2040-bit Certificate Signing Heap Buffer Overflow
Source: CVE Program / CVE List V5
Vulnerability 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.
Source: CVE Program / CVE List V5
CVSS Information
CVSS:3.1/AV:L/AC:L/PR:L/UI:N/S:U/C:L/I:L/A:H
Source: CVE Program / CVE List V5
Vulnerability Type
堆缓冲区溢出
Source: CVE Program / CVE List V5

Affected Products

Vendor Product Affected Versions CPE Subscribe
openwrt luci 0 ~ 42d72f79cd8f057f241595abc761b39dab2d9f07 -

II. Public POCs for CVE-2026-62381

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III. Intelligence Information for CVE-2026-62381

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Vendor Advisories for CVE-2026-62381 (2)

IV. Related Vulnerabilities

Same product: luci
Same vendor: openwrt
Same weakness: CWE-122

V. Comments for CVE-2026-62381

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