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GHSA-hm2w-vr2p-hq7w: UEFI Firmware Parser has a heap out-of-bounds write in tiano decompressor ReadCLen

criticalCVSS 9.8CVE-2026-54334
uefi-firmware contains a heap out-of-bounds write vulnerability in the native tiano/EFI decompressor. in uefi_firmware/compression/Tiano/Decompress.c, ReadCLen() reads Number = GetBits(Sd, CBIT) with CBIT = 9, so Number can be as large as 511, while the destination array Sd->mCLen has NC = 510 elements. the loop writes while Index < Number without enforcing Index < NC. additionally, the CharC == 2 run-length path performs GetBits(Sd, 9) + 20, allowing up to 531 zero writes through Sd->mCLen[Index++] = 0. Reachability is through the normal parsing path: CompressedSection.process() -> efi_compressor.TianoDecompress() -> TianoDecompress() -> DecodeC() -> ReadCLen(). Minimum impact is a deterministic crash; depending on build/runtime details, the heap memory corruption may be exploitable for code execution in the context of the parsing process. this project shipped its own copy of the decompressor without the upstream EDK2 hardening for this bug class. - PR: <https://github.com/theopolis/uefi-firmware-parser/pull/145> - fix commit: <https://github.com/theopolis/uefi-firmware-parser/commit/bf3dfaa8a05675bae6ea0cbfa082ddcebfcde23e> - upstream related fixes: CVE-2017-5731, CVE-2017-5732, CVE-2017-5733, CVE-2017-5734, CVE-2017-5735

Details

Source
GitHub Security Advisories (INTL · database · site)
Severity
critical — CVSS 9.8
Published
2026-04-16
Last updated
2026-07-08
Exploitation
Not in CISA KEV at last sync

Original advisory: https://github.com/advisories/GHSA-hm2w-vr2p-hq7w

Referenced CVEs

CVECSIRTS overviewExternal
CVE-2026-54334coverage & exploitation statusNVD · CVE.org

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