Bug 2540891 (CVE-2026-95811)

Summary: CVE-2026-95811 lemonldap-ng: lemonldap-ng: Access control bypass via non-normalized request URI
Product: [Other] Security Response Reporter: OSIDB Bzimport <bzimport>
Component: vulnerabilityAssignee: Product Security DevOps Team <prodsec-dev>
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Priority: medium    
Version: unspecifiedKeywords: Security
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Hardware: All   
OS: Linux   
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A flaw was found in lemonldap-ng. The request handler evaluates security rules against raw, unnormalized web addresses while the underlying web server processes decoded and normalized paths. An authenticated attacker can exploit this discrepancy by submitting specially crafted requests containing duplicate slashes, dot segments, or encoded characters to evade path-based access controls. This issue allows unauthorized access to protected resources if the virtual host is configured with a more permissive default access policy.
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Bug Depends On: 2540978, 2540979    
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Description OSIDB Bzimport 2026-09-25 01:41:26 UTC 
Lemonldap::NG::Handler versions from 2.0.0 before 2.16.10, from 2.17.0 before 2.21.6, from 2.22.0 before 2.23.4 for Perl allow an equivalent spelling of a path to bypass the locationRules that restrict it.

The handler matches each vhost's locationRules regular expressions against REQUEST_URI, the raw request line, while the web server routes on the path it has already percent-decoded and normalized. A request that percent-encodes a character of the path, inserts dot segments, or doubles a slash therefore reaches the protected resource under a URI that no rule regexp matches, and the vhost's default rule decides access. Deny rules, identity and group conditions, and unprotect and skip rules are bypassed alike.

Only a vhost whose default rule is more permissive than its other rules is affected. An authenticated user then reaches any URL a locationRules regexp was meant to restrict, but gains no more than that default rule already grants.