Vulnerability · Published Aug 26, 2026 · Assigned by NLnet Labs
CVE-2026-19538Bypass of BLOCKED ACL items on proxy protocol port over TCP or TLS
High 8.2
In plain English
A high-severity authentication bypass by spoofing in NSD from NLnet Labs. There are no confirmed reports of exploitation so far. The chance it is exploited in the next 30 days is estimated at 0.4% (higher than 38% of all known vulnerabilities). Fixed versions are available - upgrade the affected package.
Severity (CVSS 4.0)8.2High
Exploit odds (30 days)0.4%top 61.6% of all CVEs
Exploited in the wildNo reportsCISA SSVC: none
Attack toolingNoneno public tooling known
Official description
The BLOCKED access control list items that are evaluated to deny access on the the proxy protocol port can be bypassed completely when connecting over TCP or TLS and sending the query twice on connection that is kept open.
Affected packages & fixed versions
| Ecosystem | Package | Fixed in | Advisory |
|---|---|---|---|
| Debian:12 | nsd | no fix listed | DEBIAN-CVE-2026-19538 |
| Debian:13 | nsd | no fix listed | DEBIAN-CVE-2026-19538 |
| Debian:14 | nsd | 4.15.1-1 | DEBIAN-CVE-2026-19538 |
| Ubuntu:26.10 | nsd | no fix listed | UBUNTU-CVE-2026-19538 |
Affected products (as reported)
| Vendor | Product | Versions |
|---|---|---|
| NLnet Labs | NSD | 4.8.0 – before 4.15.1 |
Weakness: CWE-290, CWE-672 · Vector: CVSS:4.0/AV:N/AC:L/AT:P/PR:N/UI:N/VC:H/VI:N/VA:N/SC:N/SI:N/SA:N
References
- https://www.nlnetlabs.nl/downloads/nsd/CVE-2026-19538.txt vendor-advisory