{"id":"CVE-2026-71887","revision":null,"records":[{"revision":"afcea7dacafe4464b8f89aa4f9ed5110","observedAt":"2026-10-23T15:48:27.903+00:00","statement":{"source":"cve-program","id":"CVE-2026-71887","aliases":[],"title":"OpenPGP data signature accepted from a signing subkey without cross-certification","description":"In Bouncy Castle for Java before 1.86, the high-level OpenPGP API accepted a data signature made by a signing subkey whose Subkey Binding signature carried no embedded Primary Key Binding (cross-certification) signature, in the case where that binding omits a Key Flags subpacket. RFC 9580 sec. 5.2.1.8 and sec. 10.1.3 require the embedded Primary Key Binding signature on any subkey that can issue signatures; it is the subkey's own statement that it belongs to the primary key it is bound under. OpenPGPCertificate resolved the subkey's key flags two different ways. isSigningKey() goes through getKeyFlags() and getApplyingSubpacket(), which falls back to the primary key's direct-key or primary User ID self-signature when the binding signature omits the subpacket, so the subkey inherited the primary's SIGN_DATA and counted as signing-capable; verifyEmbeddedPrimaryKeyBinding(), which enforces the requirement, reads the binding signature's own hashed subpackets, found no SIGN_DATA there, and returned early as a non-signing key without ever demanding the back signature. The same subkey was therefore signing-capable - so its signatures were attributed to the certificate and OpenPGPSignature.OpenPGPDocumentSignature.isValid() returned true - while being exempt from cross-certification, where GnuPG refuses the identical certificate and message. An attacker needs only the victim's public signing subkey, which is public material: they bind it to their own primary key with a Subkey Binding signature they are able to make, carrying no Key Flags and no embedded Primary Key Binding signature, which they cannot make without the subkey's private key, and a relying party verifying one of the victim's genuinely signed messages against that certificate is told the signature is valid and given the attacker's certificate as its issuer. Because a certificate's User IDs are self-asserted, a verifier that pins on the subkey's fingerprint or key ID while taking the identity from the enclosing certificate reports a real signature under an attacker-chosen identity. This is misattribution of a genuine signature rather than forgery of a new one: no private key is recovered, and the signature must be one the grafted subkey actually made. The low-level PGPSignature / PGPPublicKeyRing API performs no binding checks by design and is unaffected. Key Flags are a statement about the key the carrying signature refers to (RFC 9580 sec. 5.2.3.29), so a subkey no longer inherits them from the certificate-wide signatures of the primary key: a Subkey Binding signature that omits the subpacket now leaves the subkey with no capabilities rather than the primary's, which makes the flags the cross-certification check consults the same flags every other decision consults. Preferences and the other subpackets a direct-key signature carries are inherited as before, and the primary key itself, whose flags legitimately come from its own direct-key or User ID self-signature, is unaffected.","state":0,"publishedAt":"2026-10-03T08:39:07.997+00:00","modifiedAt":"2026-10-05T16:04:21.15+00:00","affected":[{"ecosystem":"https://www.bouncycastle.org/download/bouncy-castle-java/","name":"bcpg","ranges":[],"versions":[],"rawVersionEvidence":"{\n                    \"vendor\": \"Legion of the Bouncy Castle Inc.\",\n                    \"product\": \"BC-JAVA\",\n                    \"platforms\": [\n                        \"all\"\n                    ],\n                    \"collectionURL\": \"https://www.bouncycastle.org/download/bouncy-castle-java/\",\n                    \"packageName\": \"bcpg\",\n                    \"repo\": \"https://github.com/bcgit/bc-java\",\n                    \"packageURL\": \"pkg:maven/org.bouncycastle/bcpg-jdk18on\",\n                    \"modules\": [\n                        \"pg\"\n                    ],\n                    \"programFiles\": [\n                        \"OpenPGPCertificate\"\n                    ],\n                    \"versions\": [\n                        {\n                            \"status\": \"affected\",\n                            \"version\": \"1.81\",\n                            \"lessThan\": \"1.86\",\n                            \"versionType\": \"maven\"\n                        }\n                    ],\n                    \"defaultStatus\": \"unaffected\"\n                }"}],"metrics":[{"system":"CVSS 4.0","vector":"CVSS:4.0/AV:N/AC:L/AT:P/PR:N/UI:N/VC:N/VI:H/VA:N/SC:N/SI:N/SA:N/U:Amber","score":8.2,"severity":"HIGH"}],"references":["https://github.com/bcgit/bc-java/wiki/CVE%E2%80%902026%E2%80%9071887","https://github.com/bcgit/bc-java/commit/b51452fa48ccb578fc16b8222fce9eedf92c94d6"],"sourceUrl":"https://www.cve.org/CVERecord?id=CVE-2026-71887","license":"CVE Program Terms of Use","key":"cve-program:CVE-2026-71887","identifiers":["CVE-2026-71887"]},"retained":false,"historicalAffected":[]}],"coverage":[{"source":"cisa-kev:global","scope":"Complete CISA KEV catalog; all vendors. Missing entries do not establish absence of exploitation.","generation":"2026-11-11T16:59:37.9488152+00:00","complete":true,"records":1779,"lastAttemptAt":"2026-11-11T16:59:37.9488152+00:00","lastSuccessAt":"2026-11-11T16:59:38.1293575+00:00","error":null,"lastVerifiedAt":"2026-11-11T16:59:38.1293586+00:00","snapshotPublishedAt":null,"importing":false,"stagedRecords":0,"checkedIdentifiers":null,"expectedIdentifiers":null,"failedIdentifiers":null},{"source":"cve-program","scope":"Official CVE Program baseline and cumulative hourly delta; all vendors, published and rejected records","generation":"cve-de3b77103708811b6494d2ff7c979037d73ae579742cd1649a5c765137ae5083-20b9291a59074a85bd9fdbd9e0ff98a8d24930e69329e59e2815bc7b300e21fc","complete":true,"records":424170,"lastAttemptAt":"2026-11-11T16:57:33.0518174+00:00","lastSuccessAt":"2026-11-11T16:57:32.8751677+00:00","error":null,"lastVerifiedAt":"2026-11-11T16:57:33.0518174+00:00","snapshotPublishedAt":"2026-11-11T16:29:39+00:00","importing":false,"stagedRecords":0,"checkedIdentifiers":null,"expectedIdentifiers":null,"failedIdentifiers":null},{"source":"euvd","scope":"Rolling EUVD lookups of CVE aliases in current public OSV archives; 500 identifiers per refresh, rechecked after 48 hours. Not a global EUVD catalog. Successful not-found lookups count as checked; they do not imply withdrawal or safety. No reader inventory is sent.","generation":"enrichment-4351c3aec21c46fa943fb5060158bd33","complete":false,"records":13759,"lastAttemptAt":"2026-11-11T17:11:46.90421+00:00","lastSuccessAt":"2026-11-11T17:11:46.897+00:00","error":"8 identifier lookups failed; latest failures include HTTP 403. Other identifiers were checked independently.","lastVerifiedAt":"2026-11-11T17:11:46.897+00:00","snapshotPublishedAt":null,"importing":false,"stagedRecords":0,"checkedIdentifiers":13534,"expectedIdentifiers":13813,"failedIdentifiers":8},{"source":"first-epss:nuget","scope":"FIRST EPSS for explicit CVE aliases in the collected public NuGet archive. Not a global EPSS backfill.","generation":"2026-11-11T16:59:37.9488152+00:00","complete":true,"records":1097,"lastAttemptAt":"2026-11-11T16:59:37.9488152+00:00","lastSuccessAt":"2026-11-11T16:59:38.1301472+00:00","error":null,"lastVerifiedAt":"2026-11-11T16:59:38.1301474+00:00","snapshotPublishedAt":null,"importing":false,"stagedRecords":0,"checkedIdentifiers":null,"expectedIdentifiers":null,"failedIdentifiers":null},{"source":"nvd","scope":"Rolling NVD lookups of CVE aliases in current public OSV archives; 500 identifiers per refresh, rechecked after 48 hours. Not a global NVD catalog. Successful not-found lookups count as checked; they do not imply withdrawal or safety. No reader inventory is sent.","generation":"enrichment-9169816ed33d4259981dbb50309d6730","complete":true,"records":13753,"lastAttemptAt":"2026-11-11T16:59:52.0562868+00:00","lastSuccessAt":"2026-11-11T16:59:52.052+00:00","error":null,"lastVerifiedAt":"2026-11-11T16:59:52.052+00:00","snapshotPublishedAt":null,"importing":false,"stagedRecords":0,"checkedIdentifiers":13813,"expectedIdentifiers":13813,"failedIdentifiers":0},{"source":"osv:Go","scope":"Complete OSV Go ecosystem archive, including withdrawn and malicious-package source records; statement counts are not unique CVE counts","generation":"go-3562b6c78fd1bd0f0b55daf66a0926ae24f65e462df7f6d928caad458fc696bf","complete":true,"records":9947,"lastAttemptAt":"2026-11-11T16:59:37.8157847+00:00","lastSuccessAt":"2026-11-11T04:27:43.6877707+00:00","error":null,"lastVerifiedAt":"2026-11-11T16:59:37.8157847+00:00","snapshotPublishedAt":"2026-11-11T03:32:46+00:00","importing":false,"stagedRecords":0,"checkedIdentifiers":null,"expectedIdentifiers":null,"failedIdentifiers":null},{"source":"osv:NuGet","scope":"Complete OSV NuGet ecosystem archive, including GitHub Advisory Database records; NuGet version matching only","generation":"nuget-456002455e0ab94bb92c95476d4e6d175c104cd594749982afd96c893728ecbc","complete":true,"records":2010,"lastAttemptAt":"2026-11-11T16:57:33.208402+00:00","lastSuccessAt":"2026-11-11T02:36:58.1276999+00:00","error":null,"lastVerifiedAt":"2026-11-11T16:57:33.208402+00:00","snapshotPublishedAt":"2026-11-11T01:17:51+00:00","importing":false,"stagedRecords":0,"checkedIdentifiers":null,"expectedIdentifiers":null,"failedIdentifiers":null},{"source":"osv:crates.io","scope":"Complete OSV crates.io ecosystem archive, including withdrawn and malicious-package source records; statement counts are not unique CVE counts","generation":"crates.io-baa8362b4daf9e5f39d5563775a55935e7b442c0735d33274a921579ce4a0d66","complete":true,"records":3093,"lastAttemptAt":"2026-11-11T16:59:37.9166712+00:00","lastSuccessAt":"2026-11-11T13:00:02.5446881+00:00","error":null,"lastVerifiedAt":"2026-11-11T16:59:37.9166712+00:00","snapshotPublishedAt":"2026-11-11T12:47:47+00:00","importing":false,"stagedRecords":0,"checkedIdentifiers":null,"expectedIdentifiers":null,"failedIdentifiers":null},{"source":"osv:npm","scope":"Complete OSV npm ecosystem archive, including withdrawn and malicious-package source records; statement counts are not unique CVE counts","generation":"npm-1443070691f712910eadc1ced449c2937aded59c9a578abda33e86dec787c46b","complete":true,"records":231689,"lastAttemptAt":"2026-11-11T16:59:37.6826554+00:00","lastSuccessAt":"2026-11-11T16:59:36.20998+00:00","error":null,"lastVerifiedAt":"2026-11-11T16:59:37.6826554+00:00","snapshotPublishedAt":"2026-11-11T16:33:19+00:00","importing":false,"stagedRecords":0,"checkedIdentifiers":null,"expectedIdentifiers":null,"failedIdentifiers":null}]}