CVE-2026-25793: Github.com/slackhq/nebula Blocklist Bypass Possible Vulnerability

HIGH
Advisory Identifier: GHSA-69x3-g4r3-p962
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CWE-347
Published
Advisory Summary

CVE-2026-25793 is a HIGH blocklist bypass possible vulnerability (CWE-347: Improper Verification of Cryptographic Signature) affecting Github.com/slackhq/nebula libraries in the Go ecosystem. The issue involves blocklist bypass possible via ecdsa signature malleability. Remediation is available by upgrading affected packages to version 1.10.3.

CVE-2026-25793 at a Glance

CVE Identifier CVE-2026-25793
GHSA Identifier GHSA-69x3-g4r3-p962
Severity HIGH
CVSS v3.1 Base Score N/A
CWE Classification CWE-347: Improper Verification of Cryptographic Signature
Affected Product Github.com/slackhq/nebula
Package Ecosystem Go
Published Date
Last Updated

How to Fix CVE-2026-25793

To remediate this vulnerability, upgrade all affected Github.com/slackhq/nebula dependencies to a patched release. Both direct and transitive dependencies should be checked, as frameworks or security libraries may pull in vulnerable versions transitively.

github.com/slackhq/nebula fixed: 1.10.3 
Upgrade github.com/slackhq/nebula to 1.10.3
Verify Direct and Transitive Dependencies

Run the following command in your project directory to verify that all resolved dependencies use the patched release: 

inspect dependencies for github.com/slackhq/nebula

How to Check if You Are Affected

To determine whether your application is affected by CVE-2026-25793, inspect your project dependencies for Github.com/slackhq/nebula:

inspect dependencies for github.com/slackhq/nebula

Analyze the terminal output to locate any version of Github.com/slackhq/nebula in your dependency tree. If any resolved version matches the vulnerable ranges listed in the table below (for example, versions earlier than 1.10.3), your application is affected.

Note: Verify declared build manifests and deployed runtime container environments.

Technical Details

Vulnerability Mechanism & Technical Analysis

This vulnerability is classified under CWE-347: Improper Verification of Cryptographic Signature, where the product does not verify, or incorrectly verifies, the cryptographic signature for data. In Github.com/slackhq/nebula, software state validation or input boundaries are circumvented during processing. Review the official source advisory statement below for specific affected components, classes, and reproduction details.

Source Advisory Statement

### 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_P256` certificates 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.

CVE-2026-25793 Affected Github.com/slackhq/nebula Versions

1 component(s)
Fixed Versions:
1.10.3
Product / Package Ecosystem Affected Versions Fixed Version
github.com/slackhq/nebula
golang/github.com/slackhq/nebula
Go
≥ 1.7.0
< 1.10.3
1.10.3

References

GitHub Advisory / Wiki ADVISORY
https://github.com/slackhq/nebula/security/advisories/GHSA-69x3-g4r3-p962
NVD — CVE-2026-25793 NVD
https://nvd.nist.gov/vuln/detail/CVE-2026-25793
Security Fix Commit FIX COMMIT
https://github.com/slackhq/nebula/commit/f573e8a26695278f9d71587390fbfe0d0933aa21
Github.com/slackhq/nebula Source Repository REPOSITORY
https://github.com/slackhq/nebula

Frequently Asked Questions

What is CVE-2026-25793?
CVE-2026-25793 is a security vulnerability in Github.com/slackhq/nebula involving Blocklist Bypass possible via ECDSA Signature Malleability under CWE-347: Improper Verification of Cryptographic Signature.
Which Github.com/slackhq/nebula versions are affected?
Affected versions include releases prior to 1.10.3 across affected packages: github.com/slackhq/nebula.
What version fixes CVE-2026-25793?
Upgrading to 1.10.3 (or the latest patched release for your respective branch) resolves the vulnerability.
Is github.com/slackhq/nebula affected?
Yes, github.com/slackhq/nebula is affected in releases prior to 1.10.3. Upgrade your dependency to 1.10.3 or later.
What CWE is associated with CVE-2026-25793?
CVE-2026-25793 is classified under CWE-347: Improper Verification of Cryptographic Signature (The product does not verify, or incorrectly verifies, the cryptographic signature for data.).
How can I check Go dependencies for CVE-2026-25793?
Run the dependency tree command: 'inspect dependencies for github.com/slackhq/nebula'. This command lists direct and transitive dependencies in your build configuration so you can verify if a vulnerable version is resolved.
Machine-readable OSV JSON OSV v1.5 Schema
Normalized schema output
View Raw JSON 
{
  "schema_version" : "1.4.0",
  "id" : "GHSA-69x3-g4r3-p962",
  "modified" : "2026-02-07T00:33:38Z",
  "published" : "2026-02-06T20:05:35Z",
  "aliases" : [ "CVE-2026-25793" ],
  "summary" : "Blocklist Bypass possible via ECDSA Signature Malleability",
  "details" : "### Impact\n\nWhen 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.\n\nIn order for this to affect a user or network, all of the following must be true:\n* `CURVE_P256` certificates are being used\n* There are one or more entries on the blocklist\n* The certificates for those entries are signed by a trusted CA and not expired\n* An attacker has a copy of the private key, and corresponding certificate, for one of those blocklist entries\n\n### Patches\n\nSee attached\n\n### Workarounds\n\nIf 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.\n\nRotating out all CAs that have signed hosts on the blocklist will also prevent exploitation of this vulnerability.",
  "severity" : [ {
    "type" : "CVSS_V4",
    "score" : "CVSS:4.0/AV:N/AC:L/AT:P/PR:L/UI:N/VC:H/VI:H/VA:N/SC:N/SI:N/SA:N"
  } ],
  "affected" : [ {
    "package" : {
      "ecosystem" : "Go",
      "name" : "github.com/slackhq/nebula"
    },
    "ranges" : [ {
      "type" : "ECOSYSTEM",
      "events" : [ {
        "introduced" : "1.7.0"
      }, {
        "fixed" : "1.10.3"
      } ]
    } ],
    "database_specific" : {
      "last_known_affected_version_range" : "<= 1.10.2"
    }
  } ],
  "references" : [ {
    "type" : "WEB",
    "url" : "https://github.com/slackhq/nebula/security/advisories/GHSA-69x3-g4r3-p962"
  }, {
    "type" : "ADVISORY",
    "url" : "https://nvd.nist.gov/vuln/detail/CVE-2026-25793"
  }, {
    "type" : "WEB",
    "url" : "https://github.com/slackhq/nebula/commit/f573e8a26695278f9d71587390fbfe0d0933aa21"
  }, {
    "type" : "PACKAGE",
    "url" : "https://github.com/slackhq/nebula"
  } ],
  "database_specific" : {
    "cwe_ids" : [ "CWE-347" ],
    "severity" : "HIGH",
    "github_reviewed" : true,
    "github_reviewed_at" : "2026-02-06T20:05:35Z",
    "nvd_published_at" : "2026-02-06T23:15:54Z"
  }
}