PYSEC-2026-3393

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Import Source
https://github.com/pypa/advisory-database/blob/main/vulns/uefi-firmware/PYSEC-2026-3393.yaml
JSON Data
https://api.osv.dev/v1/vulns/PYSEC-2026-3393
Aliases
Published
2026-07-13T15:02:48Z
Modified
2026-07-13T16:33:27Z
Severity
  • 9.8 (Critical) CVSS_V3 - CVSS:3.1/AV:N/AC:L/PR:N/UI:N/S:U/C:H/I:H/A:H CVSS Calculator
Summary
UEFI Firmware Parser has a stack out-of-bounds write in tiano decompressor MakeTable
Details

uefi-firmware contains a stack out-of-bounds write vulnerability in the native tiano/EFI decompressor. in uefi_firmware/compression/Tiano/Decompress.c, MakeTable() does not validate that bit-length values read from the compressed bitstream are within the expected range (0..16). a crafted firmware blob can supply bit lengths greater than 16, causing out-of-bounds writes to the stack-allocated Count[17] array and related decode tables.

reachability is through the normal parsing path: CompressedSection.process() -> efi_compressor.TianoDecompress() -> TianoDecompress() -> ReadPTLen() -> MakeTable().

Minimum impact is a deterministic crash; depending on build/runtime details, the stack 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.

References:

References

Affected packages

PyPI / uefi-firmware

Package

Name
uefi-firmware
View open source insights on deps.dev
Purl
pkg:pypi/uefi-firmware

Affected ranges

Type
ECOSYSTEM
Events
Introduced
0 Unknown introduced version / All previous versions are affected
Last Affected
1.12

Affected versions

1.*
1.1
1.2
1.3
1.4
1.6
1.7
1.8
1.9
1.10
1.11

Database specific

source 
"https://github.com/pypa/advisory-database/blob/main/vulns/uefi-firmware/PYSEC-2026-3393.yaml"