What is CVE-2026-25793?

CVE-2026-25793 is a high-severity vulnerability in Slack Nebula, classified under Improper Verification of Cryptographic Signature. CVSS score: 8.1/10. Published 2026-02-06.

How severe is CVE-2026-25793?

High severity. CVSS v3 base score is 8.1 out of 10.

Vulnerability in Slack Nebula

CVE-2026-25793

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.

Published 2026-02-06 · last modified 2026-06-17.

CVSS v3 metric

CVSS v3 base score 8.1 (High). Vector: CVSS:3.1/AV:N/AC:L/PR:L/UI:N/S:U/C:H/I:H/A:N.

EPSS exploit prediction

EPSS: 0.002 (5.7th percentile), scored 2026-09-30.

Very low probability of exploitation in the next 30 days; routine patching cadence is appropriate. 6th percentile — 5.7% of CVEs in the catalogue have a lower EPSS than this one. How to read EPSS.

EPSS over last 30 days · oldest: 0.001 · newest: 0.002 · change: +0.000

Affected products

Slack Nebula
Slackhq Nebula — versions >= 1.7.0, < 1.10.3

Weakness classification (CWE)

CWE-347 — Improper Verification of Cryptographic Signature

References

github.com/slackhq/nebula/security/advisories/GHSA-69x3-g4r3-p962 (Vendor Advisory)
github.com/slackhq/nebula/commit/f573e8a26695278f9d71587390fbfe0d0933aa21 (Patch)

Frequently asked questions

What is CVE-2026-25793?: CVE-2026-25793 is a high-severity vulnerability in Slack Nebula, classified under Improper Verification of Cryptographic Signature. CVSS score: 8.1/10. Published 2026-02-06.
How severe is CVE-2026-25793?: High severity. CVSS v3 base score is 8.1 out of 10.