Bug 2491590 (CVE-2026-12490)

Summary: CVE-2026-12490 nsd: Bypass of client certificate verification with transfer over TLS
Product: [Other] Security Response Reporter: OSIDB Bzimport <bzimport>
Component: vulnerabilityAssignee: Product Security <prodsec-ir-bot>
Status: NEW --- QA Contact:
Severity: medium Docs Contact:
Priority: medium    
Version: unspecifiedCC: security-response-team
Target Milestone: ---Keywords: Security
Target Release: ---   
Hardware: All   
OS: Linux   
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Doc Text:
A flaw was found in nsd. When a 'provide-xfr' is configured with a 'tls-auth-name', the server incorrectly allows zone transfers without requiring a client certificate if the request comes over TLS on the regular 'tls-port' or over TCP on the regular port, provided other access control conditions are met. This authentication bypass allows an attacker to perform unauthorized zone transfers, leading to information disclosure.
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oVirt Team: --- RHEL 7.3 requirements from Atomic Host:
Cloudforms Team: --- Target Upstream Version:
Embargoed:
Bug Depends On: 2494181, 2494182    
Bug Blocks:    
Deadline: 2026-06-25   

Description OSIDB Bzimport 2026-06-22 23:47:38 UTC 
When a "provide-xfr" is given with a "tls-auth-name", a secondary requesting a transfer should provide a client certificate with that name. However, no client certificate is needed when the request comes in over TLS over the regular "tls-port" (and not the "tls-auth-port") or over over TCP over the regular port, when the other conditions of the "provide-xfr" rule match.

The transfer security restrictions for client certificates can be bypassed completely if the attacker can match the other access control conditions, and the "tls-auth-xfr-only" option is not explicitly set to "yes" (which it bydefault is not)