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.
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Fixes
Solution
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Workaround
No workaround given by the vendor.
References
History
Sat, 22 Aug 2026 12:45:00 +0000
| Type | Values Removed | Values Added |
|---|---|---|
| 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. | |
| Title | luci-lib-px5g 2040-bit Certificate Signing Heap Buffer Overflow | |
| First Time appeared |
Openwrt
Openwrt luci |
|
| Weaknesses | CWE-122 | |
| CPEs | cpe:2.3:a:openwrt:luci:-:*:*:*:*:*:*:* | |
| Vendors & Products |
Openwrt
Openwrt luci |
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| References |
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| Metrics |
cvssV3_1
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Projects
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Status: PUBLISHED
Assigner: VulnCheck
Published:
Updated: 2026-08-22T12:26:44.558Z
Reserved: 2026-07-13T22:40:54.412Z
Link: CVE-2026-62381
No data.
Status : Received
Published: 2026-08-22T13:16:39.957
Modified: 2026-08-22T13:16:39.957
Link: CVE-2026-62381
No data.
OpenCVE Enrichment
Updated: 2026-08-22T13:45:03Z
Weaknesses