{"id":"CVE-2026-62381","aliases":["EUVD-2026-64273","GHSA-g4fj-xr23-w9hm","GHSA-jgc3-4q3p-g6xh"],"status":"published","title":"luci-lib-px5g 2040-bit Certificate Signing Heap Buffer Overflow","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.","severity":{"version":"4.0","score":6.9,"vector":"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","level":"medium","assessor":"cna","from":"cve"},"epss":{"day":"2026-11-11","score":0.00108,"percentile":0.01187,"model":"v2026.06.15"},"facts":{"in_kev":false,"known_exploited":false,"public_exploit":false,"fix_available":false},"cwes":["CWE-122"],"published":"2026-08-22T12:26:44Z","modified":"2026-10-28T02:31:05Z","products":[{"vendor":"openwrt","product":"luci"}],"references":[{"url":"https://github.com/openwrt/luci/security/advisories/GHSA-jgc3-4q3p-g6xh","tags":["vendor-advisory","exploit","advisory"]},{"url":"https://www.vulncheck.com/advisories/luci-lib-px5g-2040-bit-certificate-signing-heap-buffer-overflow","tags":["third-party-advisory","advisory"]},{"url":"https://nvd.nist.gov/vuln/detail/CVE-2026-62381","tags":["advisory"]},{"url":"https://github.com/advisories/GHSA-g4fj-xr23-w9hm"},{"url":"https://github.com/CVEProject/cvelistV5/tree/main/cves/2026/62xxx/CVE-2026-62381.json","tags":["advisory"]},{"url":"https://github.com/openwrt/luci","tags":["package"]}],"sources":{"cve":[{"id":"CVE-2026-62381","title":"luci-lib-px5g 2040-bit Certificate Signing Heap Buffer Overflow","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.","status":"published","published":"2026-08-22T12:26:44.558Z","modified":"2026-08-24T19:50:50.874Z","cvss":[{"version":"4.0","score":6.9,"vector":"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","level":"medium","assessor":"cna"},{"version":"3.1","score":6.6,"vector":"CVSS:3.1/AV:L/AC:L/PR:L/UI:N/S:U/C:L/I:L/A:H","level":"medium","assessor":"cna"}],"cwes":["CWE-122"],"updated_at":"2026-11-02T14:20:14.999906Z"}],"euvd":[{"id":"EUVD-2026-64273","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.","status":"published","published":"2026-08-22T12:26:44Z","modified":"2026-08-24T19:50:50Z","cvss":[{"version":"4.0","score":6.9,"vector":"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","level":"medium"}],"updated_at":"2026-11-02T18:01:34.230875Z"}],"ghsa":[{"id":"GHSA-g4fj-xr23-w9hm","title":"luci-lib-px5g (LuCI) contains a heap-based buffer overflow in the native ASN.1 encoding routine...","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.","status":"published","published":"2026-08-22T15:31:02Z","modified":"2026-08-22T15:31:11Z","cvss":[{"version":"4.0","score":6.9,"vector":"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/E:X/CR:X/IR:X/AR:X/MAV:X/MAC:X/MAT:X/MPR:X/MUI:X/MVC:X/MVI:X/MVA:X/MSC:X/MSI:X/MSA:X/S:X/AU:X/R:X/V:X/RE:X/U:X","level":"medium"},{"version":"3.1","score":6.6,"vector":"CVSS:3.1/AV:L/AC:L/PR:L/UI:N/S:U/C:L/I:L/A:H","level":"medium"}],"cwes":["CWE-122"],"updated_at":"2026-11-02T15:10:51.608425Z"}],"nvd":[{"id":"CVE-2026-62381","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.","status":"published","published":"2026-08-22T13:16:39.957Z","modified":"2026-10-12T16:10:00.22Z","cvss":[{"version":"4.0","score":6.9,"vector":"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/E:X/CR:X/IR:X/AR:X/MAV:X/MAC:X/MAT:X/MPR:X/MUI:X/MVC:X/MVI:X/MVA:X/MSC:X/MSI:X/MSA:X/S:X/AU:X/R:X/V:X/RE:X/U:X","level":"medium","assessor":"secondary"},{"version":"3.1","score":6.6,"vector":"CVSS:3.1/AV:L/AC:L/PR:L/UI:N/S:U/C:L/I:L/A:H","level":"medium","assessor":"secondary"}],"cwes":["CWE-122"],"updated_at":"2026-11-02T14:12:40.665005Z"}],"osv":[{"id":"CVE-2026-62381","title":"luci-lib-px5g 2040-bit Certificate Signing Heap Buffer Overflow","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.","status":"published","published":"2026-08-22T12:26:44.558Z","modified":"2026-10-28T02:31:05.507464774Z","cvss":[{"version":"4.0","score":6.9,"vector":"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","level":"medium"}],"cwes":["CWE-122"],"updated_at":"2026-11-02T15:45:13.306117Z"}]}}