---
title: "CVE-2026-54333: UEFI Firmware Parser has a stack out-of-bounds write in tiano decompressor MakeTable"
url: https://erroneo.us/security/cve/CVE-2026-54333/
description: "CVE-2026-54333 (uefi-firmware (PyPI)): UEFI Firmware Parser parses BIOS, Intel ME, and UEFI firmware structures including volumes, file systems, and files.…"
type: vulnerability-record
section: "Security Digest"
date_published: 2026-09-14
date_modified: 2026-09-15
publisher: erroneo.us
author: erroneo.us Security Desk
cve: "CVE-2026-54333"
kev: false
cvss: 9.8
epss: 0.00801
license: All rights reserved. Quote with attribution and a link.
---

# CVE-2026-54333: UEFI Firmware Parser has a stack out-of-bounds write in tiano decompressor MakeTable

**Signal:** Critical and remotely reachable. No known exploitation yet, but it is network-reachable without credentials. (Computed from CISA KEV, EPSS and CVSS; not an editorial verdict.)

## Should you act?

- No confirmed exploitation. It is not in CISA’s KEV catalog and CISA’s SSVC assessment records no known exploitation. That can change quickly after a public write-up; re-check if you are affected.
- EPSS 0.8% , percentile 56: FIRST’s model estimates a 0.8% chance of exploitation activity in the next 30 days, higher than 56% of all scored CVEs (moderate). EPSS is a probability, not a verdict.
- Remotely reachable with no login and no user interaction. If the vulnerable service is exposed to the internet, prioritize it.
- Only applies if your dependency tree includes uefi-firmware (PyPI) <= 1.12, no fixed version listed . Check your lockfile, including transitive dependencies.

## What it is

UEFI Firmware Parser parses BIOS, Intel ME, and UEFI firmware structures including volumes, file systems, and files. Prior to 1.14, MakeTable() in uefifirmware/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 eficompressor.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

- PyPI `uefi-firmware` <= 1.12 → fixed: none listed

## Affected products (CVE record)

- theopolis uefi-firmware-parser: < 1.14

## Severity

- GitHub_M CVSS 3.1: 9.8 `CVSS:3.1/AV:N/AC:L/PR:N/UI:N/S:U/C:H/I:H/A:H`
- GitHub CVSS 3.1: 9.8 `CVSS:3.1/AV:N/AC:L/PR:N/UI:N/S:U/C:H/I:H/A:H`

## Exploitation

- CISA KEV: not listed (no confirmed in-the-wild exploitation known to CISA).
- CISA SSVC assessment: exploitation none , automatable yes , technical impact total .
- FIRST EPSS (model of 2026-10-21): 0.80% probability of exploitation activity in the next 30 days; percentile 56.

## Sources

- [GitHub Advisory GHSA-2689-5p89-6j3j](https://github.com/advisories/GHSA-2689-5p89-6j3j)
- [CVE.org record CVE-2026-54333](https://www.cve.org/CVERecord?id=CVE-2026-54333)
- [NVD entry CVE-2026-54333](https://nvd.nist.gov/vuln/detail/CVE-2026-54333)
- [github.com](https://github.com/theopolis/uefi-firmware-parser/security/advisories/GHSA-2689-5p89-6j3j)
- [github.com](https://github.com/theopolis/uefi-firmware-parser/pull/145)
- [github.com](https://github.com/theopolis/uefi-firmware-parser/commit/bf3dfaa8a05675bae6ea0cbfa082ddcebfcde23e)
- [github.com](https://github.com/theopolis/uefi-firmware-parser/releases/tag/v1.14)

---
Source page: https://erroneo.us/security/cve/CVE-2026-54333/ · Security Digest: https://erroneo.us/security/ · More: https://erroneo.us/llms.txt