CVE-2026-25793Network attack vector

Blocklist bypass via alternate P256 signature

Published Feb 6, 2026 · Updated Feb 6, 2026

Improper P256 certificate validation in Slack Technologies Nebula 1.7.0 through 1.10.2 allows remote authenticated users to bypass blocklists. CAPool.VerifyCertificate accepted either valid ECDSA signature form while testing only one signature-derived certificate fingerprint against the blocklist. A P256 deployment with a nonempty blocklist, a trusted unexpired blocked certificate, and its private key lets the blocked peer rejoin the overlay.

CVSS severity7.6
High
EPSS probability0.14%
Next 30 days · Sep 16, 2026
Known exploitationUnconfirmed
Based on sourced intelligence
Hinoki checkNot available
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Summary

What happened

Improper P256 certificate validation in Slack Technologies Nebula 1.7.0 through 1.10.2 allows remote authenticated users to bypass blocklists. CAPool.VerifyCertificate accepted either valid ECDSA signature form while testing only one signature-derived certificate fingerprint against the blocklist. A P256 deployment with a nonempty blocklist, a trusted unexpired blocked certificate, and its private key lets the blocked peer rejoin the overlay.

The record

CVE
CVE-2026-25793
Published
Feb 6, 2026
Updated
Feb 6, 2026
Vendor
Slack Technologies
Product
Nebula
Classifications
CWE-347, T1553
Attack vector
network
Privileges
authenticated

Timeline

How it unfolded

  1. Feb 6, 2026CVE publishedPublication date reported by the CVE source.
  2. Feb 6, 2026Record 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=>= 1.7.0, < 1.10.3

What conditions does exploitation require?

Attack vectornetwork
Required privilegesauthenticated

What is affected?

Slack Technologies · Nebulaversion=>= 1.7.0, < 1.10.3

Published CVSS scores

7.6GitHub, Inc.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
8.1NVDCVSS:3.1/AV:N/AC:L/PR:L/UI:N/S:U/C:H/I:H/A:N

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-347Improper Verification of Cryptographic Signature
T1553Subvert Trust Controls

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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