UEFI Firmware Parser has a heap out-of-bounds write in tiano decompressor ReadCLen

Exploitation

No confirmed exploitation recorded. Patch Next marks exploitation only from CISA KEV.

CVSS

9.8 · CVSS:3.1/AV:N/AC:L/PR:N/UI:N/S:U/C:H/I:H/A:H

EPSS

• CVE-2026-54334: 0.80% estimated exploitation activity in the next 30 days; percentile 56.68 (FIRST EPSS, 2026-11-03). This is a model estimate, not proof of exploitation or customer exposure.

As published by the source; long descriptions are shortened.

uefi-firmware contains a heap out-of-bounds write vulnerability in the native tiano/EFI decompressor. in uefifirmware/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() - eficompressor.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:…

Published by the source

16 Apr 2026, 01:31 UTC

Last modified by the source

13 Jul 2026, 16:43 UTC

Source last checked

26 Oct 2026, 13:46 UTC

1. Revision 3 · amended · 26 Oct 2026

   Amended from ghsa record GHSA-hm2w-vr2p-hq7w

2. Revision 2 · amended · 24 Oct 2026

   Amended from osv record GHSA-hm2w-vr2p-hq7w

3. Revision 1 · created · 23 Oct 2026

   Published from ghsa record GHSA-hm2w-vr2p-hq7w

Preview the exact text before you copy it. Commands are read-only suggestions; review them before running anything.

# Patch Next advisory brief: CVE-2026-54334

Advisory: UEFI Firmware Parser has a heap out-of-bounds write in tiano decompressor ReadCLen
IDs: CVE-2026-54334, GHSA-hm2w-vr2p-hq7w
Record: https://patchnext.com/advisories/cve-2026-54334 (revision 3, source checked 26 Oct 2026, 13:46 UTC)
Inventory: none attached. This brief comes from a public page and does not say whether any deployment is affected.
Severity: Critical (CVSS 9.8)
Exploitation: no confirmed exploitation recorded. Patch Next confirms exploitation only from CISA KEV.
Vendor response: Vendor response not established. A vendor fix does not mean a deployment is fixed.

## Affected components
- PyPI uefi-firmware: affected <= 1.12

## Suggested inspection (read-only)
- `python -m pip show uefi-firmware`: prints the installed version. Run with the environment that serves production active.

## Supported action
No complete vendor fix is recorded. Follow the primary source's mitigation guidance and check this record again before closing anything.

## Required regression checks
- Run the test suite and a production build.
- Exercise the features that depend on uefi-firmware.
- Repeat the inspection and confirm that only fixed versions remain installed.

## Rollback considerations
- Keep the previous lockfile and deployment artifact. Rolling back reinstates the vulnerable version, so apply any documented mitigation while you fix forward.

## Unresolved questions
- Which deployments run an affected version?
- Exploitation status can change. Check again before lowering the priority.
- Mark the work resolved only after the fixed version is verified in production.

## Sources
- Verified: https://github.com/advisories/GHSA-hm2w-vr2p-hq7w (GitHub-reviewed advisory GHSA-hm2w-vr2p-hq7w lists affected ranges: PyPI uefi-firmware >=0 <=1.12)
- Verified: https://osv.dev/vulnerability/GHSA-hm2w-vr2p-hq7w (OSV record GHSA-hm2w-vr2p-hq7w lists affected ranges: PyPI uefi-firmware >=0 <=1.12)

Commands are suggestions: review each one before running it.