# CVE-2026-101338: NSD stack buffer overflow in SVCB/HTTPS record parsing

Source: https://junglewise.ai/threats/cve-2026-101338-when-a-svcb-or-https-rr-has-filled-the-wire-format-rdata-up-to  
Publisher: Junglewise Threat Intelligence, https://junglewise.ai/threats  
Published: 2026-10-14. Updated: 2026-10-16  
License: CC BY 4.0 with a link back

CVE-2026-101338 · Severity: info · Published 2026-10-14

NSD is an authoritative DNS nameserver that processes zone files containing DNS records. A specially crafted SVCB or HTTPS DNS record in a zone file can cause a stack buffer overflow, potentially allowing an attacker to execute arbitrary commands on the DNS server. The vulnerability requires the attacker to directly provide or control the zone file fed to NSD.

Technologies: [NLnet Labs NSD](https://junglewise.ai/threats/technologies/nlnet-labs-nsd). Vendors: [NLnet Labs](https://junglewise.ai/threats/vendors/nlnet-labs).

## Quick answers

**Is CVE-2026-101338 exploited in the wild?** No. Junglewise Threat Intelligence has no report of CVE-2026-101338 being exploited in the wild.

**How severe is CVE-2026-101338?** Informational severity, published 14 October 2026.

**Which products and versions are affected?** NLnet Labs NSD 4.10.0 through 4.15.2.

**Is there a fix for CVE-2026-101338?** Yes: fixed in NSD 4.15.3. Until then: Apply the patch from https://nlnetlabs.nl/downloads/nsd/patch_CVE-2026-101338.diff to NSD 4.15.2 source and rebuild, or upgrade to NSD 4.15.3 or later. Restrict zone file provisioning to trusted sources and validate zone files before feeding them to NSD. Junglewise finds every place you run it, drafts the upgrade and applies it once you approve.

**How is CVE-2026-101338 attacked?** It is attacked over the network, in a hosted service.

**Am I affected by CVE-2026-101338?** Check whether you run NLnet Labs NSD at an affected version. Junglewise does that check for you around the clock: connect your code, cloud and domains, and it matches new vulnerabilities like this one against what you actually run and tells you when one reaches you.

## How to fix

- Fixed in NSD 4.15.3

Apply the patch from https://nlnetlabs.nl/downloads/nsd/patch_CVE-2026-101338.diff to NSD 4.15.2 source and rebuild, or upgrade to NSD 4.15.3 or later. Restrict zone file provisioning to trusted sources and validate zone files before feeding them to NSD.

## Technical details

When parsing SVCB or HTTPS records, if the wire format RDATA fills to the maximum size and an additional ECH parameter is present, an out-of-bounds stack write occurs. The base64 decoder then writes attacker-controlled data of unlimited size beyond the buffer limit. This requires direct control or manipulation of the zone file input to NSD, not through secondary zone transfers that NSD itself generates.

## Affected products

- NLnet Labs NSD 4.10.0 through 4.15.2

## Timeline

- 2026-10-14: disclosed

## References

- [https://www.nlnetlabs.nl/downloads/nsd/CVE-2026-101338.txt](https://www.nlnetlabs.nl/downloads/nsd/CVE-2026-101338.txt)

## Related threats

- [NSD stack buffer overflow in RDATA parsing](https://junglewise.ai/threats/cve-2026-101341-tokens-of-text-in-rdata-of-for-example-txt-records-under-32)
- [NSD stack overflow in HIP resource record parsing](https://junglewise.ai/threats/cve-2026-101339-a-hip-resource-record-that-fills-the-rdata-near-or-at-is-limit)
- [NSD stack buffer overflow in base64 RDATA parsing](https://junglewise.ai/threats/cve-2026-101337-when-base64-data-is-split-up-in-pieces-of-3-character-or-less)