CVE-2026-109399

HIGH 8.1

SWUpdate through 2026.05.1 CMS Signature Verification Bypass via Embedded Intermediates

CVSS Score

8.1

EPSS Score

0.0%

EPSS Percentile

0th

SWUpdate through 2026.05.1 contains an improper certificate validation vulnerability in crypto/swupdate_cms_verify_openssl.c that trusts untrusted X.509 certificates embedded in CMS SignedData for chain building. Attackers holding a signing key from a sibling intermediate under the same root can embed that intermediate in the signature to install malicious updates.

CWE	CWE-295
Vendor	sbabic
Product	swupdate
Published	Oct 12, 2026

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CVSS v3 Breakdown

CVSS:3.1/AV:N/AC:H/PR:N/UI:N/S:U/C:H/I:H/A:H

Attack Vector

Network

Attack Complexity

High

Privileges Required

None

User Interaction

None

Scope

Unchanged

Confidentiality

High

Integrity

High

Availability

High

Affected Versions

sbabic / swupdate

0 ≤ 2026.05.1

References

NVD ↗ CVE.org ↗ EPSS Data ↗

groups.google.com: https://groups.google.com/g/swupdate/c/dsoMcGFnEns github.com: https://github.com/sbabic/swupdate/commit/e66c5640664a31668926a24c0c84b6b6570dc0d9 github.com: https://github.com/sbabic/swupdate/blob/2026.05.1/crypto/swupdate_cms_verify_openssl.c github.com: https://github.com/sbabic/swupdate vulncheck.com: https://www.vulncheck.com/advisories/swupdate-through-2026.05.1-cms-signature-verification-bypass-via-embedded-intermediates

Credits

David Gstir (sigma star gmbh) Richard Weinberger (sigma star gmbh)