CVE-2026-54333: Uefi firmware UEFI Firmware Parser Has A Vulnerability

CRITICAL
Advisory Identifier: GHSA-2689-5p89-6j3j
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CVSS 9.8
CWE-787
Published
Advisory Summary

CVE-2026-54333 is a CRITICAL (CVSS 9.8) uefi firmware parser has a vulnerability (CWE-787: Out-of-bounds Write) affecting Uefi firmware libraries in the PyPI ecosystem. The issue involves uefi firmware parser has a stack out-of-bounds write in tiano decompressor maketable. Remediation is available in the latest vendor maintenance releases.

CVE-2026-54333 at a Glance

CVE Identifier CVE-2026-54333
GHSA Identifier GHSA-2689-5p89-6j3j
Severity CRITICAL
CVSS v3.1 Base Score 9.8
CWE Classification CWE-787: Out-of-bounds Write
Affected Product Uefi firmware
Package Ecosystem PyPI
Published Date
Last Updated

Security Impact

CVSS: 9.8

The security impact metrics below are parsed directly from the CVSS v3.1 vector string (CVSS:3.1/AV:N/AC:L/PR:N/UI:N/S:U/C:H/I:H/A:H).

Attack Vector Network (AV:N)
Attack Complexity Low (AC:L)
Privileges Required None (PR:N)
User Interaction None (UI:N)
Scope Unchanged (S:U)
Confidentiality High (C:H)
Integrity High (I:H)
Availability High (A:H)

How to Fix CVE-2026-54333

To remediate this vulnerability, upgrade all affected Uefi firmware dependencies to a patched release. Both direct and transitive dependencies should be checked, as frameworks or security libraries may pull in vulnerable versions transitively.

uefi-firmware fixed: Latest secure release 
pip install uefi-firmware>=Latest secure release
Verify Direct and Transitive Dependencies

Run the following command in your project directory to verify that all resolved dependencies use the patched release: 

pip show uefi-firmware

How to Check if You Are Affected

To determine whether your Python environment is affected by CVE-2026-54333, inspect your installed packages using pip:

pip show uefi-firmware

Analyze the terminal output to locate any version of Uefi firmware in your dependency tree. If any resolved version matches the vulnerable ranges listed in the table below (for example, versions earlier than the patched release), your application is affected.

Note: The pip show uefi-firmware command checks currently installed packages in your active Python environment.

Technical Details

Vulnerability Mechanism & Technical Analysis

This vulnerability is classified under CWE-787: Out-of-bounds Write, where the product writes data past the end, or before the beginning, of the intended buffer. In Uefi firmware, software state validation or input boundaries are circumvented during processing. Review the official source advisory statement below for specific affected components, classes, and reproduction details.

Source Advisory Statement

`uefi-firmware` contains a stack out-of-bounds write vulnerability in the native tiano/EFI decompressor. in `uefi_firmware/compression/Tiano/Decompress.c`, `MakeTable()` does not validate that bit-length values read from the compressed bitstream are within the expected range (`0..16`). a crafted firmware blob can supply bit lengths greater than `16`, causing out-of-bounds writes to the stack-allocated `Count[17]` array and related decode tables. reachability is through the normal parsing path: `CompressedSection.process()` -> `efi_compressor.TianoDecompress()` -> `TianoDecompress()` -> `ReadPTLen()` -> `MakeTable()`. Minimum impact is a deterministic crash; depending on build/runtime details, the stack 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. References: - PR: <https://github.com/theopolis/uefi-firmware-parser/pull/145> - fix commit: <https://github.com/theopolis/uefi-firmware-parser/commit/bf3dfaa8a05675bae6ea0cbfa082ddcebfcde23e> - upstream related fixes: CVE-2017-5731, CVE-2017-5732, CVE-2017-5733, CVE-2017-5734, CVE-2017-5735

CVE-2026-54333 Affected Uefi firmware Versions

1 component(s)
Product / Package Ecosystem Affected Versions Fixed Version
uefi-firmware
pypi/uefi-firmware
PyPI
≤ 1.12

References

GitHub Advisory / Wiki ADVISORY
https://github.com/theopolis/uefi-firmware-parser/security/advisories/GHSA-2689-5p89-6j3j
Uefi firmware Source Repository REPOSITORY
https://github.com/theopolis/uefi-firmware-parser/pull/145
Security Fix Commit FIX COMMIT
https://github.com/theopolis/uefi-firmware-parser/commit/bf3dfaa8a05675bae6ea0cbfa082ddcebfcde23e
Uefi firmware Source Repository REPOSITORY
https://github.com/theopolis/uefi-firmware-parser

Frequently Asked Questions

What is CVE-2026-54333?
CVE-2026-54333 is a security vulnerability in Uefi firmware involving UEFI Firmware Parser has a stack out-of-bounds write in tiano decompressor MakeTable under CWE-787: Out-of-bounds Write.
Which Uefi firmware versions are affected?
Affected versions include releases prior to current release patches across affected packages: uefi-firmware.
What version fixes CVE-2026-54333?
Upgrading to current release patches (or the latest patched release for your respective branch) resolves the vulnerability.
Is uefi-firmware affected?
Yes, uefi-firmware is affected in releases prior to Latest secure release. Upgrade your dependency to Latest secure release or later.
What is the CVSS score of CVE-2026-54333?
CVE-2026-54333 has a CVSS v3.1 base score of 9.8 (CRITICAL) with vector string CVSS:3.1/AV:N/AC:L/PR:N/UI:N/S:U/C:H/I:H/A:H.
What CWE is associated with CVE-2026-54333?
CVE-2026-54333 is classified under CWE-787: Out-of-bounds Write (The product writes data past the end, or before the beginning, of the intended buffer.).
How can I check PyPI dependencies for CVE-2026-54333?
Run the dependency tree command: 'pip show uefi-firmware'. This command lists direct and transitive dependencies in your build configuration so you can verify if a vulnerable version is resolved.
Machine-readable OSV JSON OSV v1.5 Schema
Normalized schema output
View Raw JSON 
{
  "schema_version" : "1.4.0",
  "id" : "GHSA-2689-5p89-6j3j",
  "modified" : "2026-07-08T17:32:51Z",
  "published" : "2026-04-16T01:30:48Z",
  "aliases" : [ "CVE-2026-54333" ],
  "summary" : "UEFI Firmware Parser has a stack out-of-bounds write in tiano decompressor MakeTable",
  "details" : "`uefi-firmware` contains a stack out-of-bounds write vulnerability in the native tiano/EFI decompressor. in `uefi_firmware/compression/Tiano/Decompress.c`, `MakeTable()` does not validate that bit-length values read from the compressed bitstream are within the expected range (`0..16`). a crafted firmware blob can supply bit lengths greater than `16`, causing out-of-bounds writes to the stack-allocated `Count[17]` array and related decode tables.\n\nreachability is through the normal parsing path: `CompressedSection.process()` -> `efi_compressor.TianoDecompress()` -> `TianoDecompress()` -> `ReadPTLen()` -> `MakeTable()`.\n\nMinimum impact is a deterministic crash; depending on build/runtime details, the stack 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.\n\nReferences:\n\n- PR: <https://github.com/theopolis/uefi-firmware-parser/pull/145>\n- fix commit: <https://github.com/theopolis/uefi-firmware-parser/commit/bf3dfaa8a05675bae6ea0cbfa082ddcebfcde23e>\n- upstream related fixes: CVE-2017-5731, CVE-2017-5732, CVE-2017-5733, CVE-2017-5734, CVE-2017-5735",
  "severity" : [ {
    "type" : "CVSS_V3",
    "score" : "CVSS:3.1/AV:N/AC:L/PR:N/UI:N/S:U/C:H/I:H/A:H"
  } ],
  "affected" : [ {
    "package" : {
      "ecosystem" : "PyPI",
      "name" : "uefi-firmware"
    },
    "ranges" : [ {
      "type" : "ECOSYSTEM",
      "events" : [ {
        "introduced" : "0"
      }, {
        "last_affected" : "1.12"
      } ]
    } ]
  } ],
  "references" : [ {
    "type" : "WEB",
    "url" : "https://github.com/theopolis/uefi-firmware-parser/security/advisories/GHSA-2689-5p89-6j3j"
  }, {
    "type" : "WEB",
    "url" : "https://github.com/theopolis/uefi-firmware-parser/pull/145"
  }, {
    "type" : "WEB",
    "url" : "https://github.com/theopolis/uefi-firmware-parser/commit/bf3dfaa8a05675bae6ea0cbfa082ddcebfcde23e"
  }, {
    "type" : "PACKAGE",
    "url" : "https://github.com/theopolis/uefi-firmware-parser"
  } ],
  "database_specific" : {
    "cwe_ids" : [ "CWE-787" ],
    "severity" : "CRITICAL",
    "github_reviewed" : true,
    "github_reviewed_at" : "2026-04-16T01:30:48Z",
    "nvd_published_at" : null
  }
}