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MEDIUM severity

CVE-2025-62820 — nebula

MEDIUMFix: slackhq/nebula#1493

CVE-2025-62820 is a medium-severity (CVSS 4.9) CWE-420 vulnerability in github.com/slackhq/nebula. A fix is available for github.com/slackhq/nebula — see the affected versions and patch details below.

Slack Nebula may accept arbitrary source IP addresses

Also known asGHSA-x6fh-7qmf-69xhGO-2025-4068
Published
Updated
Affected
1 pkg
Patched
1 / 1
Exploits
None indexed
Exploitation data as of Nov 4, 2026 · OSV.dev, NVD, FIRST.org (EPSS)

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-2025-62820.

EPSS Exploitation Probability

via FIRST.org ↗
0.2%probability of exploitation in next 30 days
Lower Risk0.00%
Lower risk than most CVEs13th percentile — riskier than 13% of all scored CVEsHighest risk
0.00%0.24%0.48%0.72%0.0%0.2%May 26Sep 26Nov 26

Probability of exploitation in the next 30 days, from FIRST.org EPSS.

How urgent is this, really

Where this sits among everything scored

Real-World Exposure

1 pkg affected
🐹github.com/slackhq/nebula

Real-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

Slack Nebula before 1.9.7 mishandles CIDR in some configurations and thus accepts arbitrary source IP addresses within the Nebula network.

Affected Packages

1 total 1 fixed
EcosystemPackageVulnerable rangeFix
🐹Gogithub.com/slackhq/nebula≥ 1.9.4&&< 1.9.71.9.7go get github.com/slackhq/nebula@v1.9.7

Detection & mitigation playbook

Open-source dependency

  1. Detect

    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.

  2. Fix

    Update github.com/slackhq/nebula to 1.9.7 or later, then make sure no transitive (indirect) dependency still pins the vulnerable range — O3 confirms CVE-2025-62820 is resolved across your whole dependency graph.

  3. 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.

Frequently Asked Questions

Slack Nebula before 1.9.7 mishandles CIDR in some configurations and thus accepts arbitrary source IP addresses within the Nebula network.
O3 Security · Impact-Aware SCA

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CVE-2025-62820: nebula — Fixed in 1.9.7