UEFI Firmware Parser: Heap out-of-bounds write in tiano decompressor `ReadCLen`
Key facts
- Attack vector
- Network
- Privileges required
- None
- User interaction
- None
- Attack complexity
- Low
- Impact type
- Code execution
- Confidentiality · integrity · availability
- High · High · High
- Fix status
- Fixed
Attack profile from CVSS 3.1 · CNA. Fix status from CNA and GitHub. Impact type from CWE-787 and the CVSS impact.
Summary
UEFI Firmware Parser parses BIOS, Intel ME, and UEFI firmware structures including volumes, file systems, and files. Prior to 1.14, ReadCLen() in uefi_firmware/compression/Tiano/Decompress.c reads Number from GetBits(Sd, CBIT) with CBIT = 9 and can obtain 511 entries for the 510-element Sd->mCLen heap array because its loop does not enforce Index < NC. The CharC == 2 run-length path can additionally request up to 531 zero writes through Sd->mCLen[Index++] = 0. The normal CompressedSection.process() to efi_compressor.TianoDecompress() to TianoDecompress() to DecodeC() to ReadCLen() parsing path therefore permits crafted Tiano or EFI compressed firmware to corrupt heap memory, deterministically crash the parsing process, and potentially execute code depending on build and runtime details. This issue is fixed in version 1.14.
Why it matters now
SSVC decision points
CISA ADP · SSVC 2.0.3
- Exploitation
- None
- Automatable
- Yes
- Technical impact
- Total
The decision (Track, Attend, Act) also depends on your mission and well-being impact; see CISA's SSVC guide.
Affected products
| Vendor | Product | Affected versions | Fixed in | Status | Source |
|---|---|---|---|---|---|
| theopolis | uefi-firmware-parser | before 1.14 | 1.14 | Patch available | CNA |
| — | uefi-firmware (PyPI) | up to 1.12 | — | No fix listed | GHSA-hm2w-vr2p-hq7w |
- uefi-firmware-parser Vendortheopolis Affected before 1.14 Fixed in 1.14 Patch available CNA
- uefi-firmware (PyPI) Vendor— Affected up to 1.12 Fixed in — No fix listed GHSA-hm2w-vr2p-hq7w
Remediation
- Fix · CNA uefi-firmware-parser (theopolis) Fixed in 1.14
Timeline
- 2026-10-02 Threatist record created from CVE-2026-54334
- 2026-10-03 Alias added: GHSA-hm2w-vr2p-hq7w
References
Other 5
- https://github.com/theopolis/uefi-firmware-parser/security/advisories/GHSA-hm2w-vr2p-hq7w
- https://github.com/theopolis/uefi-firmware-parser/pull/145
- https://github.com/theopolis/uefi-firmware-parser/commit/bf3dfaa8a05675bae6ea0cbfa082ddcebfcde23e
- https://github.com/theopolis/uefi-firmware-parser/releases/tag/v1.14
- https://github.com/theopolis/uefi-firmware-parser
More theopolis vulnerabilities
- TI-2026-39227 UEFI Firmware Parser: Stack out-of-bounds write in tiano decompressor MakeTable CVSS 3.1CRITICAL 9.8
Sources
- CVE-2026-54334 · CVE Program
- CVE-2026-54334 · NVD
- FIRST EPSS
- GHSA-hm2w-vr2p-hq7w · GitHub Advisory Database · CC BY 4.0
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