CVE-2026-54333 UEFI Firmware Parser: Stack out-of-bounds write in tiano decompressor MakeTable
A stack 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-2026-54333?
CVE-2026-54333 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, 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.
Weakness: CWE-787
Which versions are affected by CVE-2026-54333?
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-2026-54333?
No fix has been published for CVE-2026-54333 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-2026-54333 being exploited?
There is no known exploitation of CVE-2026-54333 in the wild and no public exploit code.
Sources
Also known as GHSA-2689-5p89-6j3j, PYSEC-2026-3393.