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VulnerabilityPublished

CVE-2025-62820: Slack Nebula · Unprotected Alternate Channel

Affects Slack NebulaSource CVE Database V5

0

Not known to be exploited · CVSS 4.9 Medium : upgrade to 1.9.7 when convenient.

Data as of 26 Oct 2026, 10:12 UTC

CVSS 3.1 base score
4.9Medium
How severe the flaw is on the 0–10 CVSS scale.
EPSS
0.2% chance of exploitation in 30 days – higher than 12% of CVEsExploit Prediction Scoring System: the likelihood attackers will use this flaw soon.
Patch
Available – fixed in 1.9.7
CVSS:3.1/AV:N/AC:H/PR:L/UI:N/S:C/C:N/I:L/A:L

Exploitation evidence

  1. Disclosed: evidence found.

    CVE published 23 Oct 2025

  2. Detectable: no evidence on record.

    No public nuclei template indexed

  3. Weaponised: no evidence on record.

    No public exploit code indexed in Metasploit or Exploit-DB

  4. Exploited in the wild: no evidence on record.

    Not in CISA KEV and no source reports exploitation

  5. Observed by OffSeq Mirage: no evidence on record.

    No attack traffic recorded by OffSeq Mirage sensors

A missing step is not evidence of safety. Sources: cve.org (opens in a new tab), the Metasploit, Exploit-DB and nuclei-templates index as of 26 Oct 2026.

What to do

Upgrade slackhq/nebula to 1.9.7.

Affected software

ProductAffectedFixed in
GitHubslackhq/nebulapkg:github/slackhq/nebulaOther threatsAffected
  • <1.9.7
Fixed in
  • 1.9.7

Check your own hosts for these packages with threat-finder (opens in a new tab), our free open-source scanner.

AI-suggested

European organizations should immediately verify their Slack Nebula version and upgrade to version 1.9.7 or later where the vulnerability is addressed. In addition, network administrators should audit CIDR configurations within Nebula to ensure strict validation of source IP addresses and restrict network segments to trusted ranges. Implement network segmentation and monitoring to detect anomalous traffic patterns indicative of IP spoofing. Employ strict access controls and limit privileges to reduce the risk of exploitation by low-privilege attackers. Regularly review Nebula logs for unusual source IP activity and consider deploying intrusion detection systems tailored to overlay network traffic. Coordinate with Slack support or security advisories for any patches or workarounds. Finally, integrate this vulnerability into incident response plans to quickly address potential exploitation attempts.

Description

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

References

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