CVE-2026-54334 UEFI Firmware Parser: Heap out-of-bounds write in tiano decompressor `ReadCLen`
A heap out-of-bounds write in the Tiano decompressor allows attackers to crash the parser or potentially execute code via crafted firmware images.
- Exploited in the wild
- Not known
- Login needed
- Not needed
- Attackable
- Over the internet
- Victim action needed
- Not needed
- Fix
- None listed
What is CVE-2026-54334?
CVE-2026-54334 is a critical memory corruption vulnerability in theopolis uefi-firmware-parser, published on 14 Sep 2026. An attacker can exploit it over the internet without logging in, with no action from the victim.
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.
Weakness: CWE-787
Which versions are affected by CVE-2026-54334?
3 open source packages ship an affected version, including uefi-firmware.
| Package | Affected | Fixed in |
|---|---|---|
uefi-firmware PyPI | All versions to 1.12 | None |
uefi-firmware PyPI | All versions to 1.12 | None |
uefi-firmware PyPI | All versions to 1.12 | None |
How do I fix CVE-2026-54334?
No fix has been published for CVE-2026-54334 yet. Limit exposure of the affected software until one is available.
Upgrade to the fixed version. Memory-safe languages, compiler hardening and fuzzing prevent most new cases. More about Memory corruption.
Is CVE-2026-54334 being exploited?
There is no known exploitation of CVE-2026-54334 in the wild and no public exploit code.
Sources
Also known as GHSA-hm2w-vr2p-hq7w, PYSEC-2026-3394.