CVE-2026-103603

Memory allocation with excessive size value in the HSS/LMS signature code (HssPublicKeyParameters, HssSignature) in Legion of the Bouncy Castle Inc. bc-csharp before 2.7.0 allows a remote unauthenticated attacker who can supply both an HSS public key and a signature to cause a denial of service through memory exhaustion via a public key encoding with an excessive level count, because the level count L read when parsing an HSS public key was not checked against the RFC 8554 maximum of 8, and signature parsing then allocated an array of L - 1 entries before reading any further signature data. A single verification can commit up to about 17 GB of memory or fail with an OutOfMemoryException.

CVSS 4.0

8.7CVSS:4.0/AV:N/AC:L/AT:N/PR:N/UI:N/VC:N/VI:N/VA:H/SC:N/SI:N/SA:N

EPSS

0.5% chance of exploitation in the next 30 days; higher than 42% of CVEs (scores of 2026-10-25)

CWE

CWE-789

Published

2026-10-02

Modified

2026-10-02

Record from

the NVD, synced 2026-10-19

References

• https://github.com/bcgit/bc-csharp/commit/f47ad47c7b5745b53d3f9ac711a5a419a272a5d7
• https://github.com/bcgit/bc-csharp/wiki/CVE-2026-103603

Check your stackJSON