{"id":"CVE-2026-103603","revision":null,"records":[{"revision":"430925e0992a4a0788b5333a02a29f37","observedAt":"2026-10-23T15:48:27.903+00:00","statement":{"source":"cve-program","id":"CVE-2026-103603","aliases":[],"title":"Unbounded HSS public key level count allows huge array allocation during signature verification","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.","state":0,"publishedAt":"2026-10-02T07:10:34.017+00:00","modifiedAt":"2026-10-02T17:44:48.251+00:00","affected":[{"ecosystem":"https://www.nuget.org/packages/BouncyCastle.Cryptography","name":"BouncyCastle.Cryptography","ranges":[],"versions":[],"rawVersionEvidence":"{\n                    \"vendor\": \"Legion of the Bouncy Castle Inc.\",\n                    \"product\": \"bc-csharp\",\n                    \"collectionURL\": \"https://www.nuget.org/packages/BouncyCastle.Cryptography\",\n                    \"packageName\": \"BouncyCastle.Cryptography\",\n                    \"repo\": \"https://github.com/bcgit/bc-csharp\",\n                    \"programFiles\": [\n                        \"crypto/src/pqc/crypto/lms/HSSPublicKeyParameters.cs\",\n                        \"crypto/src/pqc/crypto/lms/HSSSignature.cs\"\n                    ],\n                    \"versions\": [\n                        {\n                            \"status\": \"affected\",\n                            \"version\": \"0\",\n                            \"lessThan\": \"2.7.0\",\n                            \"versionType\": \"semver\"\n                        }\n                    ],\n                    \"defaultStatus\": \"unaffected\"\n                }"}],"metrics":[{"system":"CVSS 4.0","vector":"CVSS:4.0/AV:N/AC:L/AT:N/PR:N/UI:N/VC:N/VI:N/VA:H/SC:N/SI:N/SA:N","score":8.7,"severity":"HIGH"}],"references":["https://github.com/bcgit/bc-csharp/wiki/CVE-2026-103603","https://github.com/bcgit/bc-csharp/commit/f47ad47c7b5745b53d3f9ac711a5a419a272a5d7"],"sourceUrl":"https://www.cve.org/CVERecord?id=CVE-2026-103603","license":"CVE Program Terms of Use","key":"cve-program:CVE-2026-103603","identifiers":["CVE-2026-103603"]},"retained":false,"historicalAffected":[]}],"coverage":[{"source":"cisa-kev:global","scope":"Complete CISA KEV catalog; all vendors. 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