CVE-2026-54334 Overview
CVE-2026-54334 is a heap out-of-bounds write [CWE-787] in the uefi-firmware-parser Python library, which parses BIOS, Intel Management Engine (ME), and Unified Extensible Firmware Interface (UEFI) firmware structures. The flaw resides in the ReadCLen() function within uefi_firmware/compression/Tiano/Decompress.c. Crafted Tiano or EFI compressed firmware sections can overflow the 510-element Sd->mCLen heap array, corrupting adjacent heap memory. Exploitation can crash the parsing process and, depending on build and runtime conditions, enable arbitrary code execution. The issue is fixed in version 1.14.
Critical Impact
Attackers can trigger heap corruption and potential remote code execution by submitting malicious firmware images to any service or tool that invokes uefi-firmware-parser for automated analysis.
Affected Products
- uefi-firmware-parser versions prior to 1.14
- Downstream tools and firmware analysis pipelines that embed the library
- Automated malware analysis and firmware validation services parsing untrusted firmware images
Discovery Timeline
- 2026-09-14 - CVE-2026-54334 published to the National Vulnerability Database (NVD)
- 2026-09-16 - Last updated in NVD database
Technical Details for CVE-2026-54334
Vulnerability Analysis
The vulnerability affects the Tiano decompression routine used to parse compressed EFI firmware sections. During Huffman table reconstruction, ReadCLen() reads a 9-bit Number value via GetBits(Sd, CBIT). Because CBIT = 9, the value can reach 511, yet the destination array Sd->mCLen holds only 510 elements. The loop writing entries does not enforce the Index < NC boundary before dereferencing the array.
A second write path compounds the issue. When CharC == 2, a run-length branch performs Sd->mCLen[Index++] = 0 in a loop that can request up to 531 zero writes. Both paths give an attacker deterministic control over out-of-bounds heap writes adjacent to the Sd structure.
The parsing chain reaches this code through CompressedSection.process() → efi_compressor.TianoDecompress() → TianoDecompress() → DecodeC() → ReadCLen(). Any workflow invoking these entry points on untrusted input is exposed.
Root Cause
The root cause is missing bounds validation between the maximum value returned by the bit reader and the fixed-size destination buffer. The developer assumed the encoded Number field would remain within NC, but the 9-bit field permits values that exceed the array capacity.
Attack Vector
An attacker crafts a malicious Tiano or EFI compressed firmware section and delivers it to any pipeline that parses firmware with the vulnerable library. The attack requires no authentication or user interaction. Delivery vectors include supply-chain firmware updates, uploads to firmware inspection services, and offline analysis of attacker-supplied BIOS images.
For technical details, see the GitHub Security Advisory GHSA-hm2w-vr2p-hq7w and the fix commit.
Stop Remote Code Execution Before It Runs
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Stop Exploit AttemptsDetection Methods for CVE-2026-54334
Indicators of Compromise
- Unexpected crashes or segmentation faults in Python processes that invoke uefi_firmware.CompressedSection.process()
- Firmware analysis workers producing heap corruption traces referencing TianoDecompress or DecodeC
- Ingestion of firmware images from untrusted origins immediately preceding analyzer instability
Detection Strategies
- Inventory hosts and containers for installed uefi-firmware-parser packages below version 1.14 using software composition analysis tooling
- Instrument firmware analysis services with AddressSanitizer or equivalent heap protection to surface out-of-bounds writes in ReadCLen()
- Correlate malformed firmware uploads with subsequent parser worker restarts in centralized log aggregation
Monitoring Recommendations
- Forward analyzer stdout, stderr, and crash dumps to a security data lake for anomaly review
- Alert on child process termination signals originating from firmware analysis containers
- Track supply-chain telemetry for firmware images whose Tiano compressed sections declare abnormal mCLen sizes
How to Mitigate CVE-2026-54334
Immediate Actions Required
- Upgrade uefi-firmware-parser to version 1.14 or later across all systems, container images, and CI/CD pipelines
- Rebuild and redeploy any downstream tools that vendor the library or bundle it into standalone binaries
- Quarantine firmware images received from untrusted sources until analyzer hosts are patched
Patch Information
The fix is available in uefi-firmware-parser v1.14 and delivered through Pull Request #145. The patch enforces Index < NC in ReadCLen() and constrains the CharC == 2 run-length loop to prevent out-of-bounds writes to Sd->mCLen.
Workarounds
- Execute firmware parsing in ephemeral, network-isolated sandboxes with strict resource limits until patching completes
- Restrict ingestion of Tiano and EFI compressed sections at the application layer using firmware type allowlists
- Enable heap hardening features such as glibc MALLOC_CHECK_ or hardened_malloc on analysis hosts
# Configuration example
pip install --upgrade 'uefi-firmware-parser>=1.14'
pip show uefi-firmware-parser | grep -i version
Disclaimer: This content was generated using AI. While we strive for accuracy, please verify critical information with official sources.
