CVE-2026-19538: nlnet labs nsd Authentication Bypass by Spoofing
CVSS: 8.2v4.0HighAnalyzed
AliasesUBUNTU-CVE-2026-19538DEBIAN-CVE-2026-19538
Published 26-08-2026Last modified 26-08-2026
Vulnerability summary
CVE-2026-19538 is a high (CVSS 8.2) Authentication Bypass by Spoofing vulnerability in nlnet labs nsd. EPSS estimates a 0.26% chance of exploitation in the next 30 days, higher than 16.5% of scored vulnerabilities.
CVSS score
8.2/10
010
High · v4.0 (CVE.org)EPSS score
0.26%
0%100%
Low · -0.04 pp in 30 daysKEVNot listedIn no KEV catalog
RansomwareNone recordedNo known use recorded
Public exploits0No public exploits recorded
Timeline
- 26-08-2026PublishedVulnerability first disclosed.
- 26-08-2026Last modifiedVulnerability information updated.
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.
CVSS metrics
6 scores · 4 sources · 2 versionsHigh 8.2Preferred score · CVE.org (CNA)
CVSS:4.0/AV:N/AC:L/AT:P/PR:N/UI:N/VC:H/VI:N/VA:N/SC:N/SI:N/SA:NSourcesAll 3 agree
- OSV · UbuntuEcosystem advisory · calculated8.2HighCVSS:4.0/AV:N/AC:L/AT:P/PR:N/UI:N/VC:H/VI:N/VA:N/SC:N/SI:N/SA:N
- NVDNIST8.2HighCVSS:4.0/AV:N/AC:L/AT:P/PR:N/UI:N/VC:H/VI:N/VA:N/SC:N/SI:N/SA:N/E:X/CR:X/IR:X/AR:X/MAV:X/MAC:X/MAT:X/MPR:X/MUI:X/MVC:X/MVI:X/MVA:X/MSC:X/MSI:X/MSA:X/S:X/AU:X/R:X/V:X/RE:X/U:X
High 7.5Preferred score · OSV · Ubuntu (Ecosystem advisory) · calculated from vector
CVSS:3.1/AV:N/AC:L/PR:N/UI:N/S:U/C:N/I:H/A:NSourcesAll 3 agree
- OSV · DebianEcosystem advisory · calculated7.5HighCVSS:3.1/AV:N/AC:L/PR:N/UI:N/S:U/C:N/I:H/A:N
- NVDNIST7.5HighCVSS:3.1/AV:N/AC:L/PR:N/UI:N/S:U/C:N/I:H/A:N
EPSS trend
Probability
0.26%
Chance of exploitation in the next 30 days
Percentile
17%
Versus all other CVEs
30-day change
-0.04 pp
From 0.30% on 19-09-2026
19-09-202619-10-2026
EPSS score0.26%
Known exploited
Compare KEV catalogsNot in any of the 3 tracked catalogs.
Public exploits
0 foundNo public exploits indexed.
Weaknesses
CWE · root cause- CWE-290Authentication Bypass by SpoofingThis attack-focused weakness is caused by incorrectly implemented authentication schemes that are subject to spoofing attacks.
- CWE-672Operation on a Resource after Expiration or ReleaseThe product uses, accesses, or otherwise operates on a resource after that resource has been expired, released, or revoked.
Affected systems
Debian1 product
- nsdAll versions (No fix recorded) | < 4.15.1-1
Nlnet labs1 product
- nsd≥ 4.8.0, < 4.15.1
Nlnetlabs1 product
- nsd≥ 4.8.0, < 4.15.1
Ubuntu1 product
- nsdAll versions (No fix recorded)
4 vendors · 4 products
