CVE-2026-19538— Bypass of BLOCKED ACL items on proxy protocol port over TCP or TLS
Quick assessment
Affected
NLnet Labs NSD
Exploitation
No confirmed in-the-wild exploitation; assess based on exposure
Recommended action
Check the vendor advisory and references for a fixed version. If immediate upgrade is impossible, restrict exposure and increase monitoring.
当通过 TCP 或 TLS 连接并保持连接打开，且在同一个连接上发送两次查询时，可以完全绕过那些用于在代理协议端口上拒绝访问的黑名单（BLOCKED）访问控制列表项。
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I. Basic Information for CVE-2026-19538
Vulnerability Information
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Vulnerability Title
Bypass of BLOCKED ACL items on proxy protocol port over TCP or TLS
Source: CVE Program / CVE List V5
Vulnerability 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.
Source: CVE Program / CVE List V5
CVSS Information
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
Source: CVE Program / CVE List V5
Vulnerability Type
使用欺骗进行的认证绕过
Source: CVE Program / CVE List V5
Affected Products
| Vendor | Product | Affected Versions | CPE | Subscribe |
|---|---|---|---|---|
| NLnet Labs | NSD | 4.8.0 ~ 4.15.1 | - |
|
II. Public POCs for CVE-2026-19538
| # | POC Description | Source Link | Shenlong Link |
|---|
AI-Generated POC
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Other References for CVE-2026-19538 (1)
-
🔗 https://www.nlnetlabs.nl/downloads/nsd/CVE-2026-19538.txt vendor-advisory
Same Patch Batch · NLnet Labs · 2026-08-26 · 4 CVEs total
| CVE-2026-18664 | 8.2 HIGH | Wrong interpretation of ACL ranges |
| CVE-2026-19401 | 8.2 HIGH | Remote UDP DoS by sending multiple DNS Cookie options |
| CVE-2026-18916 | 6.9 MEDIUM | Remote TCP DoS by throttling the TCP receive window |
IV. Related Vulnerabilities
Same product: NSD
-
CVE-2026-19401
Remote UDP DoS by sending multiple DNS Cookie options -
CVE-2026-18916
Remote TCP DoS by throttling the TCP receive window -
CVE-2026-18664
Wrong interpretation of ACL ranges -
CVE-2026-12490
Bypass of client certificate verification with transfer over -
CVE-2026-12246
Out of bounds stack write with crafted APL RR
Same vendor: NLnet Labs
-
CVE-2026-19401
Remote UDP DoS by sending multiple DNS Cookie options -
CVE-2026-18916
Remote TCP DoS by throttling the TCP receive window -
CVE-2026-18664
Wrong interpretation of ACL ranges -
CVE-2026-56444
Degradation of resolution service when 'discard-timeout' and -
CVE-2026-56416
Possible heap buffer overflow when validator canonicalizes R
Same weakness: CWE-290
-
CVE-2026-80349
TarsWeb through 3.0.14 Authentication Bypass via Spoofed X-F -
CVE-2026-75037
Polkit authentication bypass in LACT -
CVE-2026-77337
CakePHP: Potential Authentication bypass with CookieAuthenti -
CVE-2026-75509
joserfc claim-validation bypass via array-typed single-strin -
CVE-2026-76835
OAuth2 Proxy 7.15.2 through 7.15.4 Authentication Bypass via
V. Comments for CVE-2026-19538
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