CVE-2026-25793: Nebula Has Possible Blocklist Bypass via ECDSA Signature Malleability

Severity: high (CVSS 8.1 v3.1)
Exploited in the wild: not listed in CISA KEV
EPSS: 0.1% probability of exploitation in the next 30 days
Public exploit or detection template: none known
Published: 2026-02-06 · updated 2026-06-17
Weakness: CWE-347

Description

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

slackhq nebula: from 1.7.0 before 1.10.3 — fixed in 1.10.3

How to fix

Upgrade to a fixed version: slackhq nebula 1.10.3. Check the vendor advisory for mitigations.

References

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