High [CVE-2026-12244] A specially crafted SVCB RR can cause a heap overflow of up to 65509 attacker controlled bytes.
This high-severity Red Hat Linux advisory covers CVE-2026-12244.
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Summary
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 A flaw was found in nsd. When nsd is configured as a secondary server for a zone, a remote attacker, acting as the primary server for that zone, can send a specially crafted DNS message within an AXFR (Asynchronous Full Zone Transfer) request.
This message, containing a malformed SVCB (Service Binding) resource record, can cause a heap overflow, leading to arbitrary code execution. This vulnerability poses a significant risk, especially in multi-tenant secondary DNS deployments, due to the potential for a controlled write of a large amount of data.
This can lead to arbitrary code execution on the secondary NSD server. The risk is particularly significant in multi-tenant environments where NSD serves as a secondary for multiple zones, as a compromised primary could exploit this flaw within NSD's trust boundary.
This vulnerability doesn't affect any supported Red Hat Product. Red Hat severity: Important — CVSS 8 (CVSS:3.1/AV:N/AC:H/PR:H/UI:N/S:C/C:H/I:H/A:H).
Affected versions
No affected-version range was extracted from the source record. The vendor advisory is authoritative — check it before change work.
Official advisory · medium-confidence parse· fetched 21 days ago·verify at source
Fixed versions
No fixed release is recorded yet. That does not prove no patch exists — confirm against the vendor advisory.
Official advisory · medium-confidence parse· fetched 21 days ago·verify at source
Mitigation
The source record does not include mitigation steps. That is not a statement that no fix exists — read the vendor advisory below for the authoritative guidance.
Official advisory · medium-confidence parse· fetched 21 days ago·verify at source
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