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.

EPSS: 0.001 (3.2th percentile) — read the EPSS interpretation.

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.

Affected products

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

Weakness classification (CWE)

CWE-347 — Improper Verification of Cryptographic Signature

References

security-advisories@github.com (x_refsource_CONFIRM, Vendor Advisory)
security-advisories@github.com (Patch, x_refsource_MISC)

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.