CVE-2026-101338: nlnet labs nsd Stack-based Buffer Overflow

Vulnerability summary

CVE-2026-101338 is a high (CVSS 8.7) Stack-based Buffer Overflow vulnerability in nlnet labs nsd. EPSS estimates a 0.32% chance of exploitation in the next 30 days, higher than 23.6% of scored vulnerabilities.

Timeline

1. 14-10-2026
   PublishedVulnerability first disclosed.
2. 14-10-2026
   Last modifiedVulnerability information updated.

Description

When a SVCB or HTTPS RR has filled the wire format RDATA up to the brim, another ECH parameter may overwrite the stack, and once beyond the limit, the base64 decoder can write attacker controlled data of unlimited size. Zone files which are written out by NSD itself, such as for zones for which the NSD instance is secondary, will not be formatted like this. The zone file must be fed to NSD directly, (but it could come, for example, from an operator controlled provisioning system).

• CWE-121Stack-based Buffer OverflowA stack-based buffer overflow condition is a condition where the buffer being overwritten is allocated on the stack (i.e., is a local variable or, rarely, a parameter to a function).