CVE-2025-62820Network attack vector

Authenticated source-IP spoofing via overbroad remote CIDR

Published Oct 23, 2025 · Updated Oct 23, 2025

Source-IP spoofing in Slack Technologies Nebula 1.9.4 through 1.9.6 allows remote authenticated users to impersonate overlay hosts. HostInfo.CreateRemoteCIDR uses each certificate IP entry's subnet mask when building remoteCidr instead of the address bit length, admitting the entire overlay subnet. Control of a node holding a certificate with unsafe routes or multiple IP addresses is required; spoofed UDP or TCP reset packets pass source validation, but return traffic remains routed to the legitimate peer.

CVSS severity4.9
Medium
EPSS probability0.21%
Next 30 days · Sep 16, 2026
Known exploitationUnconfirmed
Based on sourced intelligence
Hinoki checkNot available
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Summary

What happened

Source-IP spoofing in Slack Technologies Nebula 1.9.4 through 1.9.6 allows remote authenticated users to impersonate overlay hosts. HostInfo.CreateRemoteCIDR uses each certificate IP entry's subnet mask when building remoteCidr instead of the address bit length, admitting the entire overlay subnet. Control of a node holding a certificate with unsafe routes or multiple IP addresses is required; spoofed UDP or TCP reset packets pass source validation, but return traffic remains routed to the legitimate peer.

The record

CVE
CVE-2025-62820
Published
Oct 23, 2025
Updated
Oct 23, 2025
Vendor
Slack Technologies
Product
Nebula
Classifications
CWE-420, T1036
Attack vector
network
Privileges
authenticated

Timeline

How it unfolded

  1. Oct 23, 2025CVE publishedPublication date reported by the CVE source.
  2. Oct 23, 2025Record updatedLatest update available in the CVE record.

Exploitability

Present is not the same as exploitable

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Is a vulnerable build present?

Compare these published version ranges with your installed build and any vendor patches.

  1. Affected versionversion=0 <1.9.7

What conditions does exploitation require?

Attack vectornetwork
Required privilegesauthenticated

What is affected?

Slack Technologies · Nebulaversion=0 <1.9.7

Published CVSS scores

4.9MITRECVSS:3.1/AV:N/AC:H/PR:L/UI:N/S:C/C:N/I:L/A:L

CVSS describes severity. EPSS estimates exploitation probability.

Attacks

What attackers are doing with it

Daily unique IPs observed by Shadowserver honeypots for known exploited vulnerabilities (KEVs). Missing observations do not establish an absence of attacks.

Daily unique IPsNo honeypot observations are available for this CVE in the selected window.

No observations available

Sep 10, 2026Sep 16, 2026
Latest reporting daySep 16, 2026
Latest daily unique IPsUnavailable
Prior 30-day averageUnavailable
SourceShadowserver honeypots (KEV)
Vectornetwork
Privilegesauthenticated
Known exploitationUnconfirmed
Public exploitUnconfirmed

Weakness, pattern, technique

CWE-420Unprotected Alternate Channel
T1036Masquerading

Public exploit references

No public exploit references are available in this record.

Labels summarize the accepted research assessment. They do not indicate a test against your environment.

Technologies

Your stack

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Your stack

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