fail2ban up to 1.1.1 sshd filter sshd.conf input validation

CVSS Meta Temp Score
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Current Exploit Price (≈)
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CTI Interest Score
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5.8$0-$5k3.13

Summaryinfo

A vulnerability marked as critical has been reported in fail2ban up to 1.1.1. This affects an unknown part of the file config/filter.d/sshd.conf of the component sshd filter. This manipulation causes input validation. This vulnerability appears as CVE-2026-109786. The attack may be initiated remotely. There is no available exploit. It is recommended to apply a patch to fix this issue.

Detailsinfo

A vulnerability was found in fail2ban up to 1.1.1. It has been declared as critical. Affected by this vulnerability is an unknown code of the file config/filter.d/sshd.conf of the component sshd filter. The manipulation with an unknown input leads to a input validation vulnerability. The CWE definition for the vulnerability is CWE-20. The product receives input or data, but it does not validate or incorrectly validates that the input has the properties that are required to process the data safely and correctly. As an impact it is known to affect integrity, and availability. The summary by CVE is:

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.

It is possible to read the advisory at github.com. This vulnerability is known as CVE-2026-109786 since 10/13/2026. The exploitation appears to be easy. The attack can be launched remotely. The exploitation doesn't need any form of authentication. Technical details of the vulnerability are known, but there is no available exploit.

Applying the patch ddd879d22664904ace24e1255ac6571808c58187 is able to eliminate this problem.

Be aware that VulDB is the high quality source for vulnerability data.

Productinfo

Name

Version

Website

CPE 2.3info

CPE 2.2info

CVSSv4info

VulDB Vector: 🔒
VulDB Reliability: 🔍

CVSSv3info

VulDB Meta Base Score: 5.9
VulDB Meta Temp Score: 5.8

VulDB Base Score: 6.5
VulDB Temp Score: 6.2
VulDB Vector: 🔒
VulDB Reliability: 🔍

CNA Base Score: 5.3
CNA Vector (MITRE): 🔒

CVSSv2info

AVACAuCIA
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VectorComplexityAuthenticationConfidentialityIntegrityAvailability
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VulDB Base Score: 🔒
VulDB Temp Score: 🔒
VulDB Reliability: 🔍

Exploitinginfo

Class: Input validation
CWE: CWE-20
CAPEC: 🔒
ATT&CK: 🔒

Physical: No
Local: No
Remote: Yes

Availability: 🔒
Status: Not defined
Price Prediction: 🔍
Current Price Estimation: 🔒

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Threat Intelligenceinfo

Interest: 🔍
Active Actors: 🔍
Active APT Groups: 🔍

Countermeasuresinfo

Recommended: Patch
Status: 🔍

0-Day Time: 🔒

Patch: ddd879d22664904ace24e1255ac6571808c58187

Timelineinfo

10/13/2026 Advisory disclosed
10/13/2026 +0 days CVE reserved
10/13/2026 +0 days VulDB entry created
10/13/2026 +0 days VulDB entry last update

Sourcesinfo

Product: github.com

Advisory: github.com
Status: Confirmed

CVE: CVE-2026-109786 (🔒)
GCVE (CVE): GCVE-0-2026-109786
GCVE (VulDB): GCVE-100-417463

Entryinfo

Created: 10/13/2026 05:03
Changes: 10/13/2026 05:03 (64)
Complete: 🔍
Cache ID: 216::103

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