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CVE-2026-54334— UEFI Firmware Parser: Heap out-of-bounds write in tiano decompressor `ReadCLen`

Quick assessment

Affected
theopolis uefi-firmware-parser
Exploitation
No confirmed in-the-wild exploitation; assess based on exposure
Recommended action
Check the vendor advisory and references for a fixed version. If immediate upgrade is impossible, restrict exposure and increase monitoring.

UEFI 固件解析器（UEFI Firmware Parser） 用于解析 BIOS、Intel ME 以及 UEFI 固件结构，包括卷（volumes）、文件系统和文件。 在版本 1.14 之前， 中的 函数使用 读取 ，其中 。由于该函数的循环未强制检查 （NC 为 堆数组的长度，即 510），因此最多可处理 511 个条目，导致越界写入。此外，当 的游程（run-length）路径还可能通过 请求最多 531 次零值写入。 因此，正常的 → → → → 解析路径允许经过精心构造的 Tiano 或 EFI 压缩

CVSS 9.8 · Critical

Possible ATT&CK Techniques 1 AI

T1545
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I. Basic Information for CVE-2026-54334

Vulnerability Information
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Vulnerability Title
UEFI Firmware Parser: Heap out-of-bounds write in tiano decompressor `ReadCLen`
Source: CVE Program / CVE List V5
Vulnerability Description
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.
Source: CVE Program / CVE List V5
CVSS Information
CVSS:3.1/AV:N/AC:L/PR:N/UI:N/S:U/C:H/I:H/A:H
Source: CVE Program / CVE List V5
Vulnerability Type
跨界内存写
Source: CVE Program / CVE List V5

Affected Products

Vendor Product Affected Versions CPE Subscribe
theopolis uefi-firmware-parser < 1.14 -

II. Public POCs for CVE-2026-54334

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III. Intelligence Information for CVE-2026-54334

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Patches & Fixes for CVE-2026-54334 (1)

Vendor Advisories for CVE-2026-54334 (1)

Other References for CVE-2026-54334 (1)

IV. Related Vulnerabilities

Same product: uefi-firmware-parser
Same vendor: theopolis
Same weakness: CWE-787

V. Comments for CVE-2026-54334

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