9.8

CVSS Score

3.1

-

CVSS Score

Basic Information

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CVE-2026-54333

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

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

(GitHub Advisory)

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CVE-2026-54333

CVE-2026-54333:

9.8

CVSS Score

3.1

-

CVSS Score

Basic Information

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Technical Details

Package Name	Ecosystem	Vulnerable Versions	First Patched Version
uefi-firmware	pip	<= 1.12

Technical Details

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Root Cause Analysis

The vulnerability is a classic stack-based buffer overflow in the MakeTable function within the Tiano decompression module. The root cause is the lack of input validation on the BitLen array, which is read from the compressed data stream. The patch introduces a simple bounds check to ensure that the values from BitLen do not exceed the size of the Count array, thus preventing the overflow. The analysis of the provided commit bf3dfaa8a05675bae6ea0cbfa082ddcebfcde23e clearly shows the addition of this check in the MakeTable function. The call chain, as described in the vulnerability details and confirmed by analyzing the source code, flows from the public API TianoDecompress down to the vulnerable MakeTable function. Therefore, MakeTable is the directly vulnerable function, and ReadPTLen and TianoDecompress are key functions in the execution path that would appear in a runtime profile during exploitation.

Vulnerable functions

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WAF Rule

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Reasoning

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