Skip to main content
No exploitation reportedAwaiting NVD analysis

CVE-2026-109786

Arbitrary IP Banning via Username Injection in fail2ban SSHD Filter

No exploitation reported by the sources we read.

  • Published2026-10-13
  • WeaknessCWE-117

Am I affected?

With a domain, we read the version its public headers and pages expose. A distribution build can carry the fix under an older number.

Description

In fail2ban 0.10.5 through 1.1.1 before ddd879d, the sshd filter (config/filter.d/sshd.conf) accepts an "on <token>" suffix after the host address. Because OpenSSH logs the offered username verbatim, a remote unauthenticated attacker can use a username such as "x VICTIM-SOURCE-IP-ADDRESS on" to make fail2ban associate failed login attempts with an arbitrary source IP address and ban it (e.g., to block logins from a legitimate user). The default filter mode is affected.

Timeline

dates in UTC
  1. 2026-10-1303:16CVE publishedNVD

Versions per branch

Products declared by the CNA1 product

As mitre, the CNA that assigned this CVE, declared them in the CVE record; versions as written.

Source: the CNA record (CVE Program), © The MITRE Corporation,CVE Terms of UseCVE recordupdated 2026-10-13

Distribution builds and vendor advisories

Packages from OSV.dev and products from the vendors' CSAF advisories.

version not verifiedVersions not verified: read as OSV.dev and the vendors publish them, not checked against each vendor's release list.

Packages

  • fail2banUbuntu:Pro:20.04:LTSall versions · no fixed version listed
  • fail2banUbuntu:Pro:18.04:LTSall versions · no fixed version listed
  • fail2banUbuntu:Pro:16.04:LTSall versions · no fixed version listed
  • fail2banUbuntu:Pro:14.04:LTSall versions · no fixed version listed
  • fail2banUbuntu:26.10all versions · no fixed version listed
  • fail2banUbuntu:26.04:LTSall versions · no fixed version listed
  • fail2banUbuntu:24.04:LTSall versions · no fixed version listed
  • fail2banUbuntu:22.04:LTSall versions · no fixed version listed

3 more package ranges on OSV.dev

Vendor advisories

  • CVE-2026-109786 Red Hat Product Security

    fail2ban: fail2ban: Denial of Service via improper host parsing in sshd filter

Full record on NVD

Fix

No fix published by the sources we read yet. NVD record

Detection

Nuclei template
none so far
ProjectDiscovery
Exploit-DB
no entry
Exploit-DB
Proof of concept
Metasploit modules
none listed
Metasploit Framework

Sources

Identifiers

Technical details

CVSS v3 Vector
CVSS:3.1/AV:N/AC:L/PR:N/UI:N/S:U/C:N/I:N/A:L
Published
2026-10-13
Last Modified
2026-10-16
NVD status
Awaiting Analysis
GitHub Advisory
GHSA-xw36-3g63-5wfw

Frequently asked questions

What is CVE-2026-109786?

In fail2ban 0.10.5 through 1.1.1 before ddd879d, the sshd filter (config/filter.d/sshd.conf) accepts an "on <token>" suffix after the host address. Because OpenSSH logs the offered username verbatim, a remote unauthenticated attacker can use a username such as "x VICTIM-SOURCE-IP-ADDRESS on" to make fail2ban associate failed login attempts with an arbitrary source IP address and ban it (e.g., to block logins from a legitimate user). The default filter mode is affected.

Is CVE-2026-109786 actively exploited?

Active exploitation of CVE-2026-109786 has not been confirmed. Its EPSS score was 0.3% on 2026-11-09, the estimated probability of exploitation in the next 30 days.

What is the CVSS score for CVE-2026-109786?

CVE-2026-109786 has a CVSS v3 base score of 5.3 (MEDIUM severity), with vector string CVSS:3.1/AV:N/AC:L/PR:N/UI:N/S:U/C:N/I:N/A:L.

Running fail2ban? Hear about its next vulnerability

Surveillance reads the versions in your stack — a domain, a lockfile or a list — checks each CVE against the ranges its sources publish, and alerts you when one you run is exploited or enters CISA KEV. A version it cannot read stays « version not verified ».

Get alerts for this productCISA KEV additions, November 2026Search CVEs

No credit card required · No monthly cap on website lookups · 250 API requests/month

Go further

Related vulnerabilities

Same product first, then the same vendor advisory and the same publication week.

Back to CVE Database

Sources for this record