CVE catalog

CVE-2026-50252

Severity: Medium · CVSS 6.5CVSS:3.1/AV:A/AC:L/PR:N/UI:N/S:U/C:N/I:H/A:N
Published: Jul 22, 2026, 1:08:54 PM UTC
Source: [NVD] · [CVE record]
EPSS: 0.17% · Oct 27, 2026

In NLnet Labs Unbound 1.4.22 up to and including 1.25.1, UDP source port is randomized and intended to serve as a secret value that increases the entropy of DNS transactions. When resolver load balancing policies depend on the source port while their outcome is revealed this secrecy is undermined. The vulnerability arises when the load balancing policy is consistent with respect to the incoming source UDP port and IP address while heavily depending on the incoming source UDP port as a randomization source. When the SO_REUSEPORT configuration option is enabled ('so-reuseport: yes') in Unbound (by default), it meets these conditions, making it vulnerable for DNS cache poisoning attacks. Upon startup, Unbound randomly partitions the available UDP source port space into disjoint subsets of (almost) equal size, assigning each subset to a specific worker thread. When an incoming DNS query is received, the kernel’s SO_REUSEPORT load balancing mechanism deterministically assigns the query to a socket associated with a particular thread. All outgoing DNS queries generated during the resolution of that request use source ports selected exclusively from the port subset assigned to the corresponding thread. Since these port subsets are disjoint across threads, the source port observed in a resolver’s outgoing query to an authoritative name server serves as a reliable indicator of the worker thread that processed the original client query. A malicious actor can acquire the mapping between incoming UDP source ports (for a given fixed source IP address) and Unbound worker threads and leverage it to conduct DNS cache poisoning attacks by effectively lowering the random port population per thread.

Vulnerable and fixed packages

Distribution-reported package versions and fixes. These do not depend on matching against the OpenFactory package catalog.

Distribution	Package	Release	Version	Status
Debian	unbound	sid	`1.26.2-1`	fixed
Debian	unbound	forky	`1.26.2-1`	fixed
Debian	unbound	trixie	`1.22.0-2+deb13u3`	vulnerable
Debian	unbound	trixie-security	`1.26.2-0+deb13u1`	fixed
Debian	unbound	bookworm	`1.17.1-2+deb12u4`	vulnerable
Debian	unbound	bookworm-security	`1.17.1-2+deb12u3`	vulnerable
Alpine	unbound	3.22	`1.25.2-r0`	fixed
Alpine	unbound	3.23	`1.25.2-r0`	fixed
Alpine	unbound	3.24	`1.25.2-r0`	fixed
Ubuntu	unbound	pro	`1.9.0-2ubuntu1`	vulnerable
Ubuntu	unbound	pro	`1.9.0-2ubuntu2`	vulnerable
Ubuntu	unbound	pro	`1.9.4-2`	vulnerable
Ubuntu	unbound	pro	`1.9.4-2ubuntu1`	vulnerable
Ubuntu	unbound	pro	`1.9.4-2ubuntu1.1`	vulnerable
Ubuntu	unbound	pro	`1.9.4-2ubuntu1.2`	vulnerable
Ubuntu	unbound	pro	`1.9.4-2ubuntu1.3`	vulnerable
Ubuntu	unbound	pro	`1.9.4-2ubuntu1.4`	vulnerable
Ubuntu	unbound	pro	`1.9.4-2ubuntu1.5`	vulnerable
Ubuntu	unbound	pro	`1.9.4-2ubuntu1.6`	vulnerable
Ubuntu	unbound	pro	`1.9.4-2ubuntu1.8`	vulnerable
Ubuntu	unbound	pro	`1.9.4-2ubuntu1.9`	vulnerable
Ubuntu	unbound	pro	`1.9.4-2ubuntu1.11`	vulnerable
Ubuntu	unbound	pro	`1.9.4-2ubuntu1.11+esm1`	vulnerable
Ubuntu	unbound	pro	`1.9.4-2ubuntu1.11+esm2`	vulnerable
Ubuntu	unbound	pro	`1.9.4-2ubuntu1.11+esm3`	fixed
Ubuntu	unbound	22.04	`1.13.1-1ubuntu1`	vulnerable
Ubuntu	unbound	22.04	`1.13.1-1ubuntu3`	vulnerable
Ubuntu	unbound	22.04	`1.13.1-1ubuntu5`	vulnerable
Ubuntu	unbound	22.04	`1.13.1-1ubuntu5.1`	vulnerable
Ubuntu	unbound	22.04	`1.13.1-1ubuntu5.2`	vulnerable
Ubuntu	unbound	22.04	`1.13.1-1ubuntu5.3`	vulnerable
Ubuntu	unbound	22.04	`1.13.1-1ubuntu5.4`	vulnerable
Ubuntu	unbound	22.04	`1.13.1-1ubuntu5.5`	vulnerable
Ubuntu	unbound	22.04	`1.13.1-1ubuntu5.7`	vulnerable
Ubuntu	unbound	22.04	`1.13.1-1ubuntu5.8`	vulnerable
Ubuntu	unbound	22.04	`1.13.1-1ubuntu5.10`	vulnerable
Ubuntu	unbound	22.04	`1.13.1-1ubuntu5.11`	vulnerable
Ubuntu	unbound	22.04	`1.13.1-1ubuntu5.12`	vulnerable
Ubuntu	unbound	22.04	`1.13.1-1ubuntu5.13`	vulnerable
Ubuntu	unbound	22.04	`1.13.1-1ubuntu5.14`	vulnerable
Ubuntu	unbound	22.04	`1.13.1-1ubuntu5.15`	vulnerable
Ubuntu	unbound	22.04	`1.13.1-1ubuntu5.16`	vulnerable
Ubuntu	unbound	22.04	`1.13.1-1ubuntu5.17`	fixed
Ubuntu	unbound	24.04	`1.17.1-2`	vulnerable
Ubuntu	unbound	24.04	`1.18.0-2ubuntu1`	vulnerable
Ubuntu	unbound	24.04	`1.18.0-2ubuntu2`	vulnerable
Ubuntu	unbound	24.04	`1.19.1-1ubuntu1`	vulnerable
Ubuntu	unbound	24.04	`1.19.2-1ubuntu1`	vulnerable
Ubuntu	unbound	24.04	`1.19.2-1ubuntu3`	vulnerable
Ubuntu	unbound	24.04	`1.19.2-1ubuntu3.1`	vulnerable
Ubuntu	unbound	24.04	`1.19.2-1ubuntu3.2`	vulnerable
Ubuntu	unbound	24.04	`1.19.2-1ubuntu3.3`	vulnerable
Ubuntu	unbound	24.04	`1.19.2-1ubuntu3.4`	vulnerable
Ubuntu	unbound	24.04	`1.19.2-1ubuntu3.5`	vulnerable
Ubuntu	unbound	24.04	`1.19.2-1ubuntu3.6`	vulnerable
Ubuntu	unbound	24.04	`1.19.2-1ubuntu3.7`	vulnerable
Ubuntu	unbound	24.04	`1.19.2-1ubuntu3.8`	vulnerable
Ubuntu	unbound	24.04	`1.19.2-1ubuntu3.9`	vulnerable
Ubuntu	unbound	24.04	`1.19.2-1ubuntu3.10`	vulnerable
Ubuntu	unbound	24.04	`1.19.2-1ubuntu3.12`	fixed
Ubuntu	unbound	26.10	`1.24.2-1ubuntu2`	vulnerable
Ubuntu	unbound	26.10	`1.25.1-1ubuntu1`	vulnerable
Ubuntu	unbound	26.10	`1.25.1-1ubuntu3`	vulnerable
Ubuntu	unbound	26.04	`1.22.0-2ubuntu2`	vulnerable
Ubuntu	unbound	26.04	`1.22.0-2ubuntu4`	vulnerable
Ubuntu	unbound	26.04	`1.24.2-1ubuntu1`	vulnerable
Ubuntu	unbound	26.04	`1.24.2-1ubuntu2`	vulnerable
Ubuntu	unbound	26.04	`1.24.2-1ubuntu2.1`	vulnerable
Ubuntu	unbound	26.04	`1.24.2-1ubuntu2.2`	vulnerable
Ubuntu	unbound	26.04	`1.24.2-1ubuntu2.3`	vulnerable
Ubuntu	unbound	26.04	`1.24.2-1ubuntu2.4`	fixed
Cpe	unbound	Not reported	`1.25.2`	fixed

Fixed-version evidence

Distribution	Package	Type	Release	Fixed version	Urgency	Origin	Bugs
Debian	unbound	source	sid	`1.25.2-1`	not yet assigned	Not reported	Not reported
Debian	unbound	source	forky	`1.25.2-1`	not yet assigned	Not reported	Not reported
Debian	unbound	source	trixie	`1.26.1-0+deb13u1`	not yet assigned	Not reported	Not reported
Debian	unbound	source	bookworm	`(unfixed)`	not yet assigned	Not reported	Not reported
Alpine	unbound	apk	3.22	`1.25.2-r0`	Not reported	ALPINE-CVE-2026-50252	Not reported
Alpine	unbound	apk	3.23	`1.25.2-r0`	Not reported	ALPINE-CVE-2026-50252	Not reported
Alpine	unbound	apk	3.24	`1.25.2-r0`	Not reported	ALPINE-CVE-2026-50252	Not reported
Ubuntu	unbound	deb	pro	`1.9.4-2ubuntu1.11+esm3`	Not reported	UBUNTU-CVE-2026-50252	Not reported
Ubuntu	unbound	deb	22.04	`1.13.1-1ubuntu5.17`	Not reported	UBUNTU-CVE-2026-50252	Not reported
Ubuntu	unbound	deb	24.04	`1.19.2-1ubuntu3.12`	Not reported	UBUNTU-CVE-2026-50252	Not reported
Ubuntu	unbound	deb	26.04	`1.24.2-1ubuntu2.4`	Not reported	UBUNTU-CVE-2026-50252	Not reported
Cpe	unbound	cpe	Not reported	`1.25.2`	Not reported	NVD-CVE-2026-50252	Not reported

OpenFactory catalog packages

[Debian 12 (Bookworm)]

[libunbound8]Affected
Source package: [unbound]
Details (4)
- 1.17.1-2+deb12u4 · amd64 · bookworm
  Affected
  nvd · unbound · debian · bookworm; nvd · unbound · debian · 12
- 1.17.1-2+deb12u4 · arm64 · bookworm
  Affected
  nvd · unbound · debian · bookworm; nvd · unbound · debian · 12
- 1.17.1-2+deb12u3 · amd64 · bookworm-security
  Affected
  nvd · unbound · debian · bookworm; nvd · unbound · debian · 12
- 1.17.1-2+deb12u3 · arm64 · bookworm-security
  Affected
  nvd · unbound · debian · bookworm; nvd · unbound · debian · 12
[libunbound-dev]Affected
Source package: [unbound]
Details (4)
- 1.17.1-2+deb12u4 · amd64 · bookworm
  Affected
  nvd · unbound · debian · bookworm; nvd · unbound · debian · 12
- 1.17.1-2+deb12u4 · arm64 · bookworm
  Affected
  nvd · unbound · debian · bookworm; nvd · unbound · debian · 12
- 1.17.1-2+deb12u3 · amd64 · bookworm-security
  Affected
  nvd · unbound · debian · bookworm; nvd · unbound · debian · 12
- 1.17.1-2+deb12u3 · arm64 · bookworm-security
  Affected
  nvd · unbound · debian · bookworm; nvd · unbound · debian · 12
[python3-unbound]Affected
Source package: [unbound]
Details (4)
- 1.17.1-2+deb12u4 · amd64 · bookworm
  Affected
  nvd · unbound · debian · bookworm; nvd · unbound · debian · 12
- 1.17.1-2+deb12u4 · arm64 · bookworm
  Affected
  nvd · unbound · debian · bookworm; nvd · unbound · debian · 12
- 1.17.1-2+deb12u3 · amd64 · bookworm-security
  Affected
  nvd · unbound · debian · bookworm; nvd · unbound · debian · 12
- 1.17.1-2+deb12u3 · arm64 · bookworm-security
  Affected
  nvd · unbound · debian · bookworm; nvd · unbound · debian · 12
[unbound]Affected
Details (4)
- 1.17.1-2+deb12u4 · amd64 · bookworm
  Affected
  nvd · unbound · debian · bookworm; nvd · unbound · debian · 12
- 1.17.1-2+deb12u4 · arm64 · bookworm
  Affected
  nvd · unbound · debian · bookworm; nvd · unbound · debian · 12
- 1.17.1-2+deb12u3 · amd64 · bookworm-security
  Affected
  nvd · unbound · debian · bookworm; nvd · unbound · debian · 12
- 1.17.1-2+deb12u3 · arm64 · bookworm-security
  Affected
  nvd · unbound · debian · bookworm; nvd · unbound · debian · 12
[unbound-anchor]Affected
Source package: [unbound]
Details (4)
- 1.17.1-2+deb12u4 · amd64 · bookworm
  Affected
  nvd · unbound · debian · bookworm; nvd · unbound · debian · 12
- 1.17.1-2+deb12u4 · arm64 · bookworm
  Affected
  nvd · unbound · debian · bookworm; nvd · unbound · debian · 12
- 1.17.1-2+deb12u3 · amd64 · bookworm-security
  Affected
  nvd · unbound · debian · bookworm; nvd · unbound · debian · 12
- 1.17.1-2+deb12u3 · arm64 · bookworm-security
  Affected
  nvd · unbound · debian · bookworm; nvd · unbound · debian · 12
[unbound-host]Affected
Source package: [unbound]
Details (4)
- 1.17.1-2+deb12u4 · amd64 · bookworm
  Affected
  nvd · unbound · debian · bookworm; nvd · unbound · debian · 12
- 1.17.1-2+deb12u4 · arm64 · bookworm
  Affected
  nvd · unbound · debian · bookworm; nvd · unbound · debian · 12
- 1.17.1-2+deb12u3 · amd64 · bookworm-security
  Affected
  nvd · unbound · debian · bookworm; nvd · unbound · debian · 12
- 1.17.1-2+deb12u3 · arm64 · bookworm-security
  Affected
  nvd · unbound · debian · bookworm; nvd · unbound · debian · 12

[Debian 13 (Trixie)]

[libunbound8]Affected
Source package: [unbound]
Details (6)
- 1.22.0-2+deb13u3 · amd64 · trixie
  Affected · Fixed: 1.26.1-0+deb13u1
  nvd · unbound · debian · 13
- 1.22.0-2+deb13u3 · arm64 · trixie
  Affected · Fixed: 1.26.1-0+deb13u1
  nvd · unbound · debian · 13
- 1.22.0-2+deb13u3 · amd64 · trixie-security · Historical version
  Affected · Fixed: 1.26.1-0+deb13u1
  nvd · unbound · debian · 13
- 1.22.0-2+deb13u3 · arm64 · trixie-security
  Affected · Fixed: 1.26.1-0+deb13u1
  nvd · unbound · debian · 13
- 1.26.1-0+deb13u1 · amd64 · trixie-security · Historical version
  Fixed · Fixed: 1.26.1-0+deb13u1
  nvd · unbound · debian · 13
- 1.26.2-0+deb13u1 · amd64 · trixie-security
  Fixed · Fixed: 1.26.1-0+deb13u1
  nvd · unbound · debian · 13
[libunbound-dev]Affected
Source package: [unbound]
Details (6)
- 1.22.0-2+deb13u3 · amd64 · trixie
  Affected · Fixed: 1.26.1-0+deb13u1
  nvd · unbound · debian · 13
- 1.22.0-2+deb13u3 · arm64 · trixie
  Affected · Fixed: 1.26.1-0+deb13u1
  nvd · unbound · debian · 13
- 1.22.0-2+deb13u3 · amd64 · trixie-security · Historical version
  Affected · Fixed: 1.26.1-0+deb13u1
  nvd · unbound · debian · 13
- 1.22.0-2+deb13u3 · arm64 · trixie-security
  Affected · Fixed: 1.26.1-0+deb13u1
  nvd · unbound · debian · 13
- 1.26.1-0+deb13u1 · amd64 · trixie-security · Historical version
  Fixed · Fixed: 1.26.1-0+deb13u1
  nvd · unbound · debian · 13
- 1.26.2-0+deb13u1 · amd64 · trixie-security
  Fixed · Fixed: 1.26.1-0+deb13u1
  nvd · unbound · debian · 13
[python3-unbound]Affected
Source package: [unbound]
Details (6)
- 1.22.0-2+deb13u3 · amd64 · trixie
  Affected · Fixed: 1.26.1-0+deb13u1
  nvd · unbound · debian · 13
- 1.22.0-2+deb13u3 · arm64 · trixie
  Affected · Fixed: 1.26.1-0+deb13u1
  nvd · unbound · debian · 13
- 1.22.0-2+deb13u3 · amd64 · trixie-security · Historical version
  Affected · Fixed: 1.26.1-0+deb13u1
  nvd · unbound · debian · 13
- 1.22.0-2+deb13u3 · arm64 · trixie-security
  Affected · Fixed: 1.26.1-0+deb13u1
  nvd · unbound · debian · 13
- 1.26.1-0+deb13u1 · amd64 · trixie-security · Historical version
  Fixed · Fixed: 1.26.1-0+deb13u1
  nvd · unbound · debian · 13
- 1.26.2-0+deb13u1 · amd64 · trixie-security
  Fixed · Fixed: 1.26.1-0+deb13u1
  nvd · unbound · debian · 13
[unbound]Affected
Details (6)
- 1.22.0-2+deb13u3 · amd64 · trixie
  Affected · Fixed: 1.26.1-0+deb13u1
  nvd · unbound · debian · 13
- 1.22.0-2+deb13u3 · arm64 · trixie
  Affected · Fixed: 1.26.1-0+deb13u1
  nvd · unbound · debian · 13
- 1.22.0-2+deb13u3 · amd64 · trixie-security · Historical version
  Affected · Fixed: 1.26.1-0+deb13u1
  nvd · unbound · debian · 13
- 1.22.0-2+deb13u3 · arm64 · trixie-security
  Affected · Fixed: 1.26.1-0+deb13u1
  nvd · unbound · debian · 13
- 1.26.1-0+deb13u1 · amd64 · trixie-security · Historical version
  Fixed · Fixed: 1.26.1-0+deb13u1
  nvd · unbound · debian · 13
- 1.26.2-0+deb13u1 · amd64 · trixie-security
  Fixed · Fixed: 1.26.1-0+deb13u1
  nvd · unbound · debian · 13
[unbound-anchor]Affected
Source package: [unbound]
Details (6)
- 1.22.0-2+deb13u3 · amd64 · trixie
  Affected · Fixed: 1.26.1-0+deb13u1
  nvd · unbound · debian · 13
- 1.22.0-2+deb13u3 · arm64 · trixie
  Affected · Fixed: 1.26.1-0+deb13u1
  nvd · unbound · debian · 13
- 1.22.0-2+deb13u3 · amd64 · trixie-security · Historical version
  Affected · Fixed: 1.26.1-0+deb13u1
  nvd · unbound · debian · 13
- 1.22.0-2+deb13u3 · arm64 · trixie-security
  Affected · Fixed: 1.26.1-0+deb13u1
  nvd · unbound · debian · 13
- 1.26.1-0+deb13u1 · amd64 · trixie-security · Historical version
  Fixed · Fixed: 1.26.1-0+deb13u1
  nvd · unbound · debian · 13
- 1.26.2-0+deb13u1 · amd64 · trixie-security
  Fixed · Fixed: 1.26.1-0+deb13u1
  nvd · unbound · debian · 13
[unbound-host]Affected
Source package: [unbound]
Details (6)
- 1.22.0-2+deb13u3 · amd64 · trixie
  Affected · Fixed: 1.26.1-0+deb13u1
  nvd · unbound · debian · 13
- 1.22.0-2+deb13u3 · arm64 · trixie
  Affected · Fixed: 1.26.1-0+deb13u1
  nvd · unbound · debian · 13
- 1.22.0-2+deb13u3 · amd64 · trixie-security · Historical version
  Affected · Fixed: 1.26.1-0+deb13u1
  nvd · unbound · debian · 13
- 1.22.0-2+deb13u3 · arm64 · trixie-security
  Affected · Fixed: 1.26.1-0+deb13u1
  nvd · unbound · debian · 13
- 1.26.1-0+deb13u1 · amd64 · trixie-security · Historical version
  Fixed · Fixed: 1.26.1-0+deb13u1
  nvd · unbound · debian · 13
- 1.26.2-0+deb13u1 · amd64 · trixie-security
  Fixed · Fixed: 1.26.1-0+deb13u1
  nvd · unbound · debian · 13

Observed: Oct 27, 2026, 7:12:16 AM UTC

References

[CERT-Bund public advisories] · [Debian Security Tracker] · [FIRST EPSS] · [National Vulnerability Database (NVD)] · [OSV Package Vulnerability Database] · [Red Hat security advisories and VEX] · [SUSE security advisories and VEX]