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Vulnerability · Published Sep 14, 2026 · Assigned by GitHub_M

CVE-2026-54333UEFI Firmware Parser: Stack out-of-bounds write in tiano decompressor MakeTable

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, MakeTable() in uefi_firmware/compression/Tiano/Decompress.c does not validate that bit-length values read from a crafted Tiano or EFI compressed firmware bitstream remain within the expected range from 0 through 16. The normal CompressedSection.process() to efi_compressor.TianoDecompress() to TianoDecompress() to ReadPTLen() to MakeTable() parsing path can consequently write beyond the stack-allocated Count[17] array and related decode tables. The resulting stack corruption deterministically crashes the parsing process and may permit code execution depending on build and runtime details. This issue is fixed in version 1.14.

Affected packages & fixed versions

EcosystemPackageFixed inAdvisory
PyPIuefi-firmwareno fix listedGHSA-2689-5p89-6j3j
PyPIuefi-firmwareno fix listedPYSEC-2026-3393

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