Nebula is a scalable overlay networking tool. In versions from 1.7.0 to 1.10.2, when 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. This issue has been patched in version 1.10.3.
PUBLISHED5.2CWE-347
Nebula Has Possible Blocklist Bypass via ECDSA Signature Malleability
Problem type
Affected products
slackhq
nebula
>= 1.7.0, < 1.10.3 - AFFECTED
References
https://github.com/slackhq/nebula/security/advisories/GHSA-69x3-g4r3-p962
https://github.com/slackhq/nebula/security/advisories/GHSA-69x3-g4r3-p962
https://github.com/slackhq/nebula/commit/f573e8a26695278f9d71587390fbfe0d0933aa21
https://github.com/slackhq/nebula/commit/f573e8a26695278f9d71587390fbfe0d0933aa21
GitHub Security Advisories
GHSA-69x3-g4r3-p962
Blocklist Bypass possible via ECDSA Signature Malleability
https://github.com/advisories/GHSA-69x3-g4r3-p962Impact
When 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.
In order for this to affect a user or network, all of the following must be true:
CURVE_P256certificates are being used- There are one or more entries on the blocklist
- The certificates for those entries are signed by a trusted CA and not expired
- An attacker has a copy of the private key, and corresponding certificate, for one of those blocklist entries
Patches
See attached
Workarounds
If 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.
Rotating out all CAs that have signed hosts on the blocklist will also prevent exploitation of this vulnerability.
JSON source
https://cveawg.mitre.org/api/cve/CVE-2026-25793Click to expand
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