Bug 2494188

Summary: CVE-2026-12244 nsd: A specially crafted SVCB RR can cause a heap overflow of up to 65509 attacker controlled bytes. [fedora-all]
Product: [Fedora] Fedora Reporter: Marco Benatto <mbenatto>
Component: nsdAssignee: Paul Wouters <paul.wouters>
Status: NEW --- QA Contact: Fedora Extras Quality Assurance <extras-qa>
Severity: high Docs Contact:
Priority: high    
Version: rawhideCC: drjohnson1, me, paul.wouters
Target Milestone: ---Keywords: Security, SecurityTracking
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Hardware: Unspecified   
OS: Unspecified   
Whiteboard: {"flaws": ["beefe42f-ed4c-4824-860a-02f6f9514ab6"]}
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oVirt Team: --- RHEL 7.3 requirements from Atomic Host:
Cloudforms Team: --- Target Upstream Version:
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Bug Depends On:    
Bug Blocks: 2491587    

Description Marco Benatto 2026-06-29 13:49:04 UTC 
Disclaimer: Community trackers are created by Red Hat Product Security team on a best effort basis. Package maintainers are required to ascertain if the flaw indeed affects their package, before starting the update process.

If NSD is configured as secondary for a zone, the primary of that zone can crash NSD with an AXFR containing a DNS message with a special crafted SVCB RR with an rdata size of 65512, that let's an (uint16_t) variable that is used to allocate space needed for the RR wrap (because total size > 65535), causing a heap overflow. The attacker can perform a controlled (RCE class) head write of up to 65509 bytes.

Even though the data is from a configured primary inside NSD's trust boundary, we do consider the risk significant enough for multi-tenant secondary DNS deployments, given the potential severity of the attack.