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…
Does this matter?
High impact if exploited, but EPSS currently rates exploitation as unlikely (0.50%). Schedule it in the normal patch cycle and watch for a rise in EPSS or a public exploit.
Description
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
- 8.7 HIGHCVSS:4.0/AV:N/AC:L/AT:N/PR:N/UI:N/VC:N/VI:N/VA:H/SC:N/SI:N/SA:N/E:X/CR:X/IR:X/AR:X/MAV:X/MAC:X/MAT:X/MPR:X/MUI:X/MVC:X/M
- EPSS
- 0.50% probability · 43th percentile
- Public exploits
- None in Exploit-DB
- CISA KEV
- Not listed
- Weakness
- CWE-789
- Source
- 91579145-5d7b-4cc5-b925-a0262ff19630
EPSS moved from 0.4% on 2 October 2026 to 0.5% on 26 October 2026.
References
Source: NVD record, EPSS from FIRST.org, KEV from CISA, exploits from Exploit-DB. Refreshed daily. Download this record as JSON.