Quick answers
- Is CVE-2026-19538 exploited in the wild?
- No. Junglewise Threat Intelligence has no report of CVE-2026-19538 being exploited in the wild.
- How severe is CVE-2026-19538?
- High severity, with a CVSS score of 7.5, published 26 August 2026.
- Which products and versions are affected?
- NLnet Labs NSD 4.8.0 to 4.15.0.
- Is there a fix for CVE-2026-19538?
- A patch was published on 2026: NSD 4.15.1 released with patch; patch available for 4.15.0 Junglewise finds every place you run it, drafts the upgrade and applies it once you approve.
- How is CVE-2026-19538 attacked?
- It is attacked over the network.
- Am I affected by CVE-2026-19538?
- Check whether you run Nlnetlabs Nsd. 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.
Technical details
The vulnerability exists in NSD's handling of access control lists (ACLs) on the proxy protocol port. BLOCKED ACL items that should deny access over TCP or TLS connections can be completely bypassed by sending a DNS query twice on a persistent (keep-alive) connection. The root cause stems from improper validation of the proxy protocol headers or query processing logic. An unauthenticated network attacker with access to the proxy protocol port can exploit this flaw to spoof arbitrary source IP addresses, effectively bypassing all IP-based access controls applied to queries, zone transfers, and notifications. Patched versions 4.15.1 and later address this issue; a patch is also available for manual application to NSD 4.15.0.
Affected products
- NLnet Labs NSD 4.8.0 to 4.15.0
Timeline
- 2026-08-26: disclosed
- 2026: patched: NSD 4.15.1 released with patch; patch available for 4.15.0