CVE-2026-25793: Slack Nebula

High severity, CVSS 8.1. EPSS: 0.2% chance of exploitation in the next 30 days.

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.

Affected products

• Slack Nebula: from 1.7.0, before 1.10.3 (fixed in 1.10.3)

Published 2026-02-06. Last modified 2026-06-17.