{"dataType":"CVE_RECORD","dataVersion":"5.2","cveMetadata":{"cveId":"CVE-2026-103603","assignerOrgId":"91579145-5d7b-4cc5-b925-a0262ff19630","state":"PUBLISHED","assignerShortName":"bcorg","dateReserved":"2026-09-30T23:01:10.053Z","datePublished":"2026-10-02T07:10:34.017Z","dateUpdated":"2026-10-02T17:44:48.251Z"},"containers":{"cna":{"providerMetadata":{"orgId":"91579145-5d7b-4cc5-b925-a0262ff19630","shortName":"bcorg","dateUpdated":"2026-10-02T07:10:34.017Z"},"title":"Unbounded HSS public key level count allows huge array allocation during signature verification","problemTypes":[{"descriptions":[{"lang":"en","cweId":"CWE-789","description":"CWE-789 Memory Allocation with Excessive Size Value","type":"CWE"}]}],"impacts":[{"descriptions":[{"lang":"en","value":"Denial of Service (memory exhaustion during HSS signature verification)"}]}],"affected":[{"vendor":"Legion of the Bouncy Castle Inc.","product":"bc-csharp","collectionURL":"https://www.nuget.org/packages/BouncyCastle.Cryptography","packageName":"BouncyCastle.Cryptography","repo":"https://github.com/bcgit/bc-csharp","programFiles":["crypto/src/pqc/crypto/lms/HSSPublicKeyParameters.cs","crypto/src/pqc/crypto/lms/HSSSignature.cs"],"versions":[{"status":"affected","version":"0","lessThan":"2.7.0","versionType":"semver"}],"defaultStatus":"unaffected"}],"descriptions":[{"lang":"en","value":"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.","supportingMedia":[{"type":"text/html","base64":false,"value":"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."}]}],"references":[{"url":"https://github.com/bcgit/bc-csharp/wiki/CVE-2026-103603","tags":["vendor-advisory"]},{"url":"https://github.com/bcgit/bc-csharp/commit/f47ad47c7b5745b53d3f9ac711a5a419a272a5d7","tags":["patch"]}],"metrics":[{"format":"CVSS","scenarios":[{"lang":"en","value":"GENERAL"}],"cvssV4_0":{"attackVector":"NETWORK","attackComplexity":"LOW","attackRequirements":"NONE","privilegesRequired":"NONE","userInteraction":"NONE","vulnConfidentialityImpact":"NONE","subConfidentialityImpact":"NONE","vulnIntegrityImpact":"NONE","subIntegrityImpact":"NONE","vulnAvailabilityImpact":"HIGH","subAvailabilityImpact":"NONE","exploitMaturity":"NOT_DEFINED","Safety":"NOT_DEFINED","Automatable":"NOT_DEFINED","Recovery":"NOT_DEFINED","valueDensity":"NOT_DEFINED","vulnerabilityResponseEffort":"NOT_DEFINED","providerUrgency":"NOT_DEFINED","version":"4.0","baseSeverity":"HIGH","baseScore":8.7,"vectorString":"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"}}],"credits":[{"lang":"en","value":"Discovered by Claude, Anthropic's AI assistant, and triaged by the Anthropic security team in collaboration with Anthropic Research.","type":"finder"}],"source":{"discovery":"EXTERNAL"},"x_generator":{"engine":"Claude Opus 5.5"},"x_antReportIds":["ANT-2026-F7RBDSF7"]},"adp":[{"metrics":[{"other":{"type":"ssvc","content":{"timestamp":"2026-10-02T17:44:39.796207Z","id":"CVE-2026-103603","options":[{"Exploitation":"none"},{"Automatable":"yes"},{"Technical Impact":"partial"}],"role":"CISA Coordinator","version":"2.0.3"}}}],"title":"CISA ADP Vulnrichment","providerMetadata":{"orgId":"134c704f-9b21-4f2e-91b3-4a467353bcc0","shortName":"CISA-ADP","dateUpdated":"2026-10-02T17:44:48.251Z"}}]}}