UEFI Firmware Parser has a heap out-of-bounds write in tiano decompressor ReadCLen

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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

Basic information

Type
reviewed
Severity
critical
Advisory on GitHub
Open advisory ↗
Repository advisory
Open repository advisory ↗
Source code
Browse source ↗
Published (advisory)
2026-04-16 01:31:09 UTC
Updated
2026-04-16 01:31:10 UTC
GitHub reviewed
2026-04-16 01:31:09 UTC

CVSS Scores

Base score Version Severity Vector
9.8 3.1 —
CVSS:3.1/AV:N/AC:L/PR:N/UI:N/S:U/C:H/I:H/A:H Click to expand
Attack vector (AV:N)
Could be attacked over the internet or any normal routed network—not just someone sitting at the machine.
Attack complexity (AC:L)
Once they can reach the bug, pulling it off is straightforward—no weird race conditions or rare setup.
Privileges required (PR:N)
No account or special rights needed—anonymous or random user is enough.
User interaction (UI:N)
Nobody has to click “OK” or open a trap file; it can work without a victim helping.
Scope (S:U)
Damage stays in the same “trust bubble” as the broken component—no big spill into unrelated systems.
Confidentiality (C:H)
Serious risk that confidential data gets exposed in a big way.
Integrity (I:H)
They could widely tamper with or forge data—trust in the data is badly hurt.
Availability (A:H)
Could take the service down hard or make it unusable for people who depend on it.

Identifiers

Type Value
GHSA GHSA-hm2w-vr2p-hq7w ↗

CWEs

CWE id Name
CWE-787 Out-of-bounds Write

Credits

  • 1seal (finder)

Affected packages (1)

Vulnerable version ranges and first patched releases as published by GitHub.

Ecosystem Package Vulnerable range First patched Vulnerable functions
pip uefi-firmware <= 1.12 — —

References

cvelogic Threat Intelligence