CVE-2026-25793 — nebula
Fix: slackhq/nebula@f573e8aCVE-2026-25793 is a CWE-347 vulnerability in github.com/slackhq/nebula. A fix is available for github.com/slackhq/nebula — see the affected versions and patch details below.
Nebula Has Possible Blocklist Bypass via ECDSA Signature Malleability
Exploitation Status
No confirmed exploitation observed yet
- CISA’s own triage has not observed active exploitation or public proof-of-concept code for this CVE as of its last assessment.
Exploitation and automatability from CISA’s SSVC triage for CVE-2026-25793.
EPSS Exploitation Probability
EPSS (Exploit Prediction Scoring System) is a daily probability model maintained by FIRST.org. It estimates the likelihood a CVE will be exploited in production environments within the next 30 days, derived from real-world threat intelligence signals.
Real-World Exposure
github.com/slackhq/nebulaReal-time download stats are indexed for npm and PyPI packages. This vulnerability affects Go packages — download data is not available via public APIs for these ecosystems.
Description
Impact
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.
In order for this to affect a user or network, all of the following must be true:
CURVE_P256certificates are being used- There are one or more entries on the blocklist
- The certificates for those entries are signed by a trusted CA and not expired
- An attacker has a copy of the private key, and corresponding certificate, for one of those blocklist entries
Patches
See attached
Workarounds
If full copies of each certificate on the existing blocklist are available, it is possible to compute their opposite-chirality signature, and then the appropriate second fingerprint to list in the blocklist.
Rotating out all CAs that have signed hosts on the blocklist will also prevent exploitation of this vulnerability.
Affected Packages
| Ecosystem | Package | Vulnerable range | Fix |
|---|---|---|---|
| 🐹Go | github.com/slackhq/nebula | ≥ 1.7.0&&< 1.10.3 | 1.10.3go get github.com/slackhq/nebula@v1.10.3 |
Detection & mitigation playbook
Open-source dependencyDetect
Scan your dependency tree (package-lock.json, pnpm-lock.yaml, requirements.txt, go.sum, etc.) for github.com/slackhq/nebula, including transitive dependencies — a direct dependency you never call can still pull in a vulnerable version.
Fix
Update github.com/slackhq/nebula to 1.10.3 or later, then make sure no transitive (indirect) dependency still pins the vulnerable range — O3 confirms CVE-2026-25793 is resolved across your whole dependency graph.
Workarounds
If you can't upgrade right away: gate or disable the affected feature, validate untrusted input at the boundary, and avoid passing attacker-controlled data into the vulnerable path. O3's runtime protection blocks exploitation in production as an interim safeguard until the upgrade lands.
How O3 protects you
O3 Security's impact-aware SCA analyses which vulnerable code paths your application actually calls, so a match like CVE-2026-25793 can be triaged on real exposure rather than presence alone.
Tailored to CVE-2026-25793. Runtime protection reduces exposure until a permanent patch is applied and verified — it complements patching, it doesn't replace it.
Frequently Asked Questions
Is CVE-2026-25793 in your dependencies?
O3 Security finds CVE-2026-25793 across Go dependencies, including transitive ones, and its impact-aware SCA ranks findings by whether your code actually calls the vulnerable path.