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Vulnerability · Published Sep 14, 2026 · Assigned by GitHub_M

CVE-2026-54334UEFI Firmware Parser: Heap out-of-bounds write in tiano decompressor `ReadCLen`

Critical 9.8

In plain English

A critical-severity out-of-bounds write in uefi-firmware-parser from theopolis. There are no confirmed reports of exploitation so far. The chance it is exploited in the next 30 days is estimated at 0.8% (higher than 57% of all known vulnerabilities).

Severity (CVSS 3.1)9.8Critical
Exploit odds (30 days)0.8%top 43.2% of all CVEs
Exploited in the wildNo reportsCISA SSVC: none
Attack toolingNoneno public tooling known

Official description

UEFI Firmware Parser parses BIOS, Intel ME, and UEFI firmware structures including volumes, file systems, and files. Prior to 1.14, ReadCLen() in uefi_firmware/compression/Tiano/Decompress.c reads Number from GetBits(Sd, CBIT) with CBIT = 9 and can obtain 511 entries for the 510-element Sd->mCLen heap array because its loop does not enforce Index < NC. The CharC == 2 run-length path can additionally request up to 531 zero writes through Sd->mCLen[Index++] = 0. The normal CompressedSection.process() to efi_compressor.TianoDecompress() to TianoDecompress() to DecodeC() to ReadCLen() parsing path therefore permits crafted Tiano or EFI compressed firmware to corrupt heap memory, deterministically crash the parsing process, and potentially execute code depending on build and runtime details. This issue is fixed in version 1.14.

Affected packages & fixed versions

EcosystemPackageFixed inAdvisory
PyPIuefi-firmwareno fix listedGHSA-hm2w-vr2p-hq7w
PyPIuefi-firmwareno fix listedPYSEC-2026-3394

Affected products (as reported)

VendorProductVersions
theopolis uefi-firmware-parser < 1.14

Weakness: CWE-787 · Vector: CVSS:3.1/AV:N/AC:L/PR:N/UI:N/S:U/C:H/I:H/A:H

References