{"id":"CVE-2026-25793","aliases":["GHSA-69x3-g4r3-p962","GO-2026-4458"],"url":"https://o3.security/vulnerability/CVE-2026-25793","summary":"Nebula Has Possible Blocklist Bypass via ECDSA Signature Malleability","details":"### Impact\n\nWhen using P256 certificates (which is not the default configuration), it is possible to evade a blocklist entry created against the fingerprint of a certificate by using ECDSA Signature Malleability to use a copy of the certificate with a different fingerprint.\n\nIn order for this to affect a user or network, all of the following must be true:\n* `CURVE_P256` certificates are being used\n* There are one or more entries on the blocklist\n* The certificates for those entries are signed by a trusted CA and not expired\n* An attacker has a copy of the private key, and corresponding certificate, for one of those blocklist entries\n\n### Patches\n\nSee attached\n\n### Workarounds\n\nIf full copies of each certificate on the existing blocklist are available, it is possible to compute their opposite-chirality signature, and then the appropriate second fingerprint to list in the blocklist.\n\nRotating out all CAs that have signed hosts on the blocklist will also prevent exploitation of this vulnerability.","published":"2026-02-06T22:55:36.011Z","modified":"2026-08-12T03:51:35.986847494Z","cvss":null,"epss":{"score":0.00133,"percentile":0.03026,"asOf":"2026-08-24"},"cisaKev":null,"exploitsKnown":0,"affectedPackages":[{"ecosystem":"Go","name":"github.com/slackhq/nebula","fixedVersion":"1.10.3"}],"fix":{"url":"https://github.com/slackhq/nebula/commit/f573e8a26695278f9d71587390fbfe0d0933aa21","label":"slackhq/nebula@f573e8a"},"references":[{"type":"ADVISORY","url":"https://github.com/CVEProject/cvelistV5/tree/main/cves/2026/25xxx/CVE-2026-25793.json"},{"type":"ADVISORY","url":"https://github.com/slackhq/nebula/security/advisories/GHSA-69x3-g4r3-p962"},{"type":"ADVISORY","url":"https://nvd.nist.gov/vuln/detail/CVE-2026-25793"},{"type":"FIX","url":"https://github.com/slackhq/nebula/commit/f573e8a26695278f9d71587390fbfe0d0933aa21"},{"type":"PACKAGE","url":"https://github.com/slackhq/nebula"}],"provenance":{"sources":["OSV.dev","FIRST.org (EPSS)"],"lastVerified":"2026-08-12T03:51:35.986847494Z"}}