CVE-2026-25793: Nebula is a scalable overlay networking tool

Routine

HIGH 8.1UPGRADE

CVE-2026-25793 is a high-severity flaw (CVSS 8.1) affecting nebula. Below: why it ranks where it does, which versions are affected, what to do, and the exact commands.

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.

Why this priority

High severity

A fixed release or distro patch exists.

Risk facts

CVSS score	8.1 (High)
Attack vector	Network (remote)
Attack complexity	Low
Privileges needed	Low
User interaction	None
EPSS exploit chance	0.1% (top 96%)
CISA exploited list	No
Weakness	CWE-347
Published	2026-02-06
Last modified	2026-06-17

Publisher (CNA): GitHub, Inc. · Vendor: slack

Last updated 2026-06-17 · Sources: CVE Program, NVD, CISA KEV, EPSS and vendor advisories · How we score

Am I affected?

Timeline

2026-02-06 23:15 UTCPublished CVE record published
2026-06-17 10:25 UTCUpdated Record last modified

slack nebula UPGRADE

Affected: >= 1.7.0 and < 1.10.3

Fixed in: 1.10.3

Safe to downgrade to: a release before 1.7.0

1. Check installed version

apt-cache policy nebula || rpm -q nebula || nebula --version

2. UPGRADE to 1.10.3 (Debian / Ubuntu)

sudo apt update && sudo apt install --only-upgrade nebula

2. UPGRADE (RHEL / Amazon Linux / Fedora)

sudo dnf upgrade nebula

Note

Distros often backport fixes without changing the version number. Confirm with the distro advisory or changelog.

3. If no update is available yet, DOWNGRADE to a release before 1.7.0 (Debian / Ubuntu)

apt-cache madison nebula sudo apt install nebula=<VERSION_BEFORE_1.7.0> sudo apt-mark hold nebula

3. If no update is available yet, DOWNGRADE (RHEL / Amazon Linux / Fedora)

dnf --showduplicates list nebula sudo dnf downgrade nebula-<VERSION_BEFORE_1.7.0> sudo dnf versionlock add nebula

Downgrade risk

Downgrading can break dependent software and may reopen older bugs. Read the distro advisory first and test on a non-production host.

After downgrade

Restart the service, and keep the package held until a fixed release ships.

Verify at the official source NVD · CVE Program · Report a problem with this page
Scores and fixes here are computed automatically from those and other public sources. Confirm with the vendor advisory before changing production systems.

Quick answers

How do I fix CVE-2026-25793?

nebula: upgrade to 1.10.3. Exact commands for each OS are on this page.

Is CVE-2026-25793 being exploited?

CVE-2026-25793 is not on the CISA Known Exploited Vulnerabilities list at the time of the last update. Check again, as this can change.

What does CVE-2026-25793 affect?

CVE-2026-25793 affects nebula. Severity is high (CVSS 8.1). 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 certificat

How urgent is CVE-2026-25793?

Priority 29/100. High severity

Software pages

Slack vulnerabilities

References

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