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Fencer Intel
critical 9.8

CVE-2026-86426 json

LibreNMS before 26.8.0 Authentication Bypass via API Token Type Confusion

published 2mo ago modified last mo. also EUVD-2026-72384 , GHSA-cvq8-gqfq-3mvg

Unreviewed: the maintainers' own advisory

Published by the maintainers on their GitHub repository librenms/librenms. GitHub has not reviewed it into the GitHub Advisory Database, so the affected packages and versions are the maintainers' word. Read the full advisory on GitHub.

cvss
9.8
version 3.1, NVD
cisa kev
Not listed
not in CISA's catalog
epss
4.4%
EPSS 4.4% chance of exploitation in 30 days, percentile 91%
public exploits
0
none known

Summary

LibreNMS before 26.8.0 contains an authentication bypass vulnerability in the REST API that allows unauthenticated attackers to access protected endpoints by sending numeric values instead of string tokens. Attackers can exploit MySQL type coercion by sending small integers like 0 through 9 to match token hashes, gaining access to API functionality including device credentials and administrative features that enable remote code execution through alert templates.

Patch / fix

  • librenms librenms 26.8.0

Is CVE-2026-86426 in your stack? Fencer shows which of your repositories are affected as soon as an advisory lands, and opens the fix as a pull request.

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CISA SSVC

Exploitation
Proof of concept is public
Automatable
no
Technical impact
total
Assessed
2mo ago

Exploit prediction

4.36% chance of exploitation in the next 30 days, higher than 91% of all scored CVEs (FIRST EPSS, 2026-11-11).

Exploits and checks

  • github.com https://github.com/librenms/librenms/security/advisories/GHSA-cvq8-gqfq-3mvg referenced PoC, tagged "exploit" by a source, unverified

CVSS scores

assigned by version score vector
CNA 4.0 9.2 CVSS:4.0/AV:N/AC:L/AT:P/PR:N/UI:N/VC:H/VI:H/VA:H/SC:N/SI:N/SA:N
CNA 4.0 9.2 CVSS:4.0/AV:N/AC:L/AT:P/PR:N/UI:N/VC:H/VI:H/VA:H/SC:N/SI:N/SA:N/E:X/CR:X/IR:X/AR:X/MAV:X/MAC:X/MAT:X/MPR:X/MUI:X/MVC:X/MVI:X/MVA:X/MSC:X/MSI:X/MSA:X/S:X/AU:X/R:X/V:X/RE:X/U:X
NVD 3.1 9.8 CVSS:3.1/AV:N/AC:L/PR:N/UI:N/S:U/C:H/I:H/A:H

Affected products

  • librenms librenms

Classification

Weakness

References

Sources

Fencer Intel keeps one entry per vulnerability: the CVE id wins, then GHSA, and records that alias each other are merged, except that two CVEs always keep separate entries. The same data is available as JSON.

The maintainers of librenms/librenms published their own advisory on GitHub. Reviewed sources take precedence over it.