CVE-2026-101338 Stack overwrite from a specially crafted and formatted SVCB or HTTPS RR
A stack overwrite in NSD allows attackers to execute arbitrary code or cause denial of service via crafted SVCB or HTTPS resource records.
- Exploited in the wild
- Not known
- Login needed
- Any signed-in user
- Attackable
- Over the internet
- Victim action needed
- Not needed
- Fix
- Available
What is CVE-2026-101338?
CVE-2026-101338 is a high-severity memory corruption vulnerability in NLnet Labs NSD, published on 14 Oct 2026. Any signed-in user can exploit it over the network, with no action from the victim.
Official 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).
Weakness: CWE-121
Which versions are affected by CVE-2026-101338?
How do I fix CVE-2026-101338?
Apply the vendor's patch.
Upgrade to the fixed version. Memory-safe languages, compiler hardening and fuzzing prevent most new cases. More about Memory corruption.
Is CVE-2026-101338 being exploited?
There is no known exploitation of CVE-2026-101338 in the wild and no public exploit code.
Sources
Also known as ALPINE-CVE-2026-101338, DEBIAN-CVE-2026-101338, GHSA-r5wh-92fx-cv6j, UBUNTU-CVE-2026-101338.