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9.8
UEFI Firmware Parser Can Crash or Allow Malicious Code Execution
GHSA-hm2w-vr2p-hq7w
Summary
The UEFI Firmware Parser contains a vulnerability that can cause a crash or potentially allow malicious code to be executed. This issue affects systems that use the Tiano decompressor. To protect your systems, update to the latest version of the UEFI Firmware Parser, which includes a fix for this issue.
What to do
No fix is available yet. Check with your software vendor for updates.
Affected software
| Ecosystem | Vendor | Product | Affected versions |
|---|---|---|---|
| PyPI | teddy reed | uefi-firmware | <= 1.12 |
Original title
UEFI Firmware Parser has a heap out-of-bounds write in tiano decompressor ReadCLen
Original description
`uefi-firmware` contains a heap out-of-bounds write vulnerability in the native tiano/EFI decompressor. in `uefi_firmware/compression/Tiano/Decompress.c`, `ReadCLen()` reads `Number = GetBits(Sd, CBIT)` with `CBIT = 9`, so `Number` can be as large as `511`, while the destination array `Sd->mCLen` has `NC = 510` elements. the loop writes while `Index < Number` without enforcing `Index < NC`. additionally, the `CharC == 2` run-length path performs `GetBits(Sd, 9) + 20`, allowing up to `531` zero writes through `Sd->mCLen[Index++] = 0`.
Reachability is through the normal parsing path: `CompressedSection.process()` -> `efi_compressor.TianoDecompress()` -> `TianoDecompress()` -> `DecodeC()` -> `ReadCLen()`.
Minimum impact is a deterministic crash; depending on build/runtime details, the heap 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.
- 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
Reachability is through the normal parsing path: `CompressedSection.process()` -> `efi_compressor.TianoDecompress()` -> `TianoDecompress()` -> `DecodeC()` -> `ReadCLen()`.
Minimum impact is a deterministic crash; depending on build/runtime details, the heap 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.
- 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
osv CVSS3.1
9.8
Vulnerability type
CWE-787
Out-of-bounds Write
Published: 16 Apr 2026 · Updated: 16 Apr 2026 · First seen: 16 Apr 2026