DEBIAN-CVE-2026-50251
In NLnet Labs Unbound up to and including version 1.25.1, when 'unwanted-reply-threshold' is enabled (set to any value greater than zero), glue records of 0.0.0.0/::0 can short-circuit Unbound, on systems that can direct such traffic, by issuing DNS queries and receiving seemingly unwanted replies since the remote IP does not match the original source IP of 0.0.0.0/::0. This behavior keeps on looping for the glue records and pushing the counter to the configured 'unwanted-reply-threshold' that triggers a defensive cache clear. A malicious actor who controls a delegation that returns in-bailiwick glue of 0.0.0.0/::0 can drive the counter to the limit of 'unwanted-reply-threshold' to the threshold and trigger a cache clean of the message and rrset caches; at will, indefinitely, without sending a single spoofed packet. The iterator uses the 0.0.0.0/::0 glue, and a system that can route this (e.g., Linux kernel routes the datagram over loopback), Unbound's own listener answers from 127.0.0.1. Because of the mismatch of 0.0.0.0 and 127.0.0.1, in this example, Unbound accounts the reply as an unwanted (probably spoofed) answer. The counter resets to zero on every cache flush, so the attack loops forever.
DEBIAN-CVE-2026-50251
Primary source · Revision 1
Imported from structured advisory data. Source references identify upstream records or fields; verify affected versions and your deployed configuration.
Security context
Source reference: osv:DEBIAN-CVE-2026-50251
unbound
Source reference: /affected/0/package/name
- Affected versions
- 1.17.1-2
Source reference:
/affected/0/versions1.17.1-2+deb12u1Source reference:
/affected/0/versions1.17.1-2+deb12u2Source reference:
/affected/0/versions1.17.1-2+deb12u3Source reference:
/affected/0/versions1.17.1-2+deb12u4Source reference:
/affected/0/versions1.17.1-2+loong64Source reference:
/affected/0/versions1.18.0-1Source reference:
/affected/0/versions1.18.0-2Source reference:
/affected/0/versions1.19.1-1Source reference:
/affected/0/versions1.19.2-1Source reference:
/affected/0/versions1.20.0-1Source reference:
/affected/0/versions1.21.1-1Source reference:
/affected/0/versions1.22.0-1Source reference:
/affected/0/versions1.22.0-2Source reference:
/affected/0/versions1.23.1-1Source reference:
/affected/0/versions1.24.0-1Source reference:
/affected/0/versions1.24.0-2Source reference:
/affected/0/versions1.24.1-1Source reference:
/affected/0/versions1.24.1-2Source reference:
/affected/0/versions1.24.2-1Source reference:
/affected/0/versions1.25.0-1Source reference:
/affected/0/versions1.25.1-1Source reference:
/affected/0/versions1.25.2-1Source reference:
/affected/0/versions1.26.0-1Source reference:
/affected/0/versions1.26.0-2Source reference:
/affected/0/versions1.26.1-1Source reference:
/affected/0/versions1.26.2-1Source reference:
/affected/0/versions - Fixed versions
- Not stated in this record
- Prerequisites
- Not stated in this record
unbound
Source reference: /affected/1/package/name
- Affected versions
- 1.22.0-2
Source reference:
/affected/1/versions1.22.0-2+deb13u1Source reference:
/affected/1/versions1.22.0-2+deb13u2Source reference:
/affected/1/versions1.22.0-2+deb13u3Source reference:
/affected/1/versions1.23.1-1Source reference:
/affected/1/versions1.24.0-1Source reference:
/affected/1/versions1.24.0-2Source reference:
/affected/1/versions1.24.1-1Source reference:
/affected/1/versions1.24.1-2Source reference:
/affected/1/versions1.24.2-1Source reference:
/affected/1/versions1.25.0-1Source reference:
/affected/1/versions1.25.1-1Source reference:
/affected/1/versions1.25.2-1Source reference:
/affected/1/versions1.26.0-1Source reference:
/affected/1/versions1.26.0-2Source reference:
/affected/1/versions - Fixed versions
- 1.26.1-0+deb13u1
Source reference:
/affected/1/ranges - Prerequisites
- Not stated in this record
unbound
Source reference: /affected/2/package/name
- Affected versions
- 1.22.0-2
Source reference:
/affected/2/versions1.23.1-1Source reference:
/affected/2/versions1.24.0-1Source reference:
/affected/2/versions1.24.0-2Source reference:
/affected/2/versions1.24.1-1Source reference:
/affected/2/versions1.24.1-2Source reference:
/affected/2/versions1.24.2-1Source reference:
/affected/2/versions1.25.0-1Source reference:
/affected/2/versions1.25.1-1Source reference:
/affected/2/versions - Fixed versions
- 1.25.2-1
Source reference:
/affected/2/ranges - Prerequisites
- Not stated in this record
Structured affected-version data
Original package identities and version rules from this source.
[
{
"ranges": [
{
"type": "ECOSYSTEM",
"events": [
{
"introduced": "0"
}
]
}
],
"package": {
"name": "unbound",
"purl": "pkg:deb/debian/unbound?arch=source&distro=bookworm",
"ecosystem": "Debian:12"
},
"versions": [
"1.17.1-2",
"1.17.1-2+deb12u1",
"1.17.1-2+deb12u2",
"1.17.1-2+deb12u3",
"1.17.1-2+deb12u4",
"1.17.1-2+loong64",
"1.18.0-1",
"1.18.0-2",
"1.19.1-1",
"1.19.2-1",
"1.20.0-1",
"1.21.1-1",
"1.22.0-1",
"1.22.0-2",
"1.23.1-1",
"1.24.0-1",
"1.24.0-2",
"1.24.1-1",
"1.24.1-2",
"1.24.2-1",
"1.25.0-1",
"1.25.1-1",
"1.25.2-1",
"1.26.0-1",
"1.26.0-2",
"1.26.1-1",
"1.26.2-1"
],
"database_specific": {
"source": "https://storage.googleapis.com/debian-osv/debian-cve-osv/DEBIAN-CVE-2026-50251.json"
},
"ecosystem_specific": {
"urgency": "not yet assigned"
}
},
{
"ranges": [
{
"type": "ECOSYSTEM",
"events": [
{
"introduced": "0"
},
{
"fixed": "1.26.1-0+deb13u1"
}
]
}
],
"package": {
"name": "unbound",
"purl": "pkg:deb/debian/unbound?arch=source&distro=trixie",
"ecosystem": "Debian:13"
},
"versions": [
"1.22.0-2",
"1.22.0-2+deb13u1",
"1.22.0-2+deb13u2",
"1.22.0-2+deb13u3",
"1.23.1-1",
"1.24.0-1",
"1.24.0-2",
"1.24.1-1",
"1.24.1-2",
"1.24.2-1",
"1.25.0-1",
"1.25.1-1",
"1.25.2-1",
"1.26.0-1",
"1.26.0-2"
],
"database_specific": {
"source": "https://storage.googleapis.com/debian-osv/debian-cve-osv/DEBIAN-CVE-2026-50251.json"
},
"ecosystem_specific": {
"urgency": "not yet assigned"
}
},
{
"ranges": [
{
"type": "ECOSYSTEM",
"events": [
{
"introduced": "0"
},
{
"fixed": "1.25.2-1"
}
]
}
],
"package": {
"name": "unbound",
"purl": "pkg:deb/debian/unbound?arch=source&distro=forky",
"ecosystem": "Debian:14"
},
"versions": [
"1.22.0-2",
"1.23.1-1",
"1.24.0-1",
"1.24.0-2",
"1.24.1-1",
"1.24.1-2",
"1.24.2-1",
"1.25.0-1",
"1.25.1-1"
],
"database_specific": {
"source": "https://storage.googleapis.com/debian-osv/debian-cve-osv/DEBIAN-CVE-2026-50251.json"
},
"ecosystem_specific": {
"urgency": "not yet assigned"
}
}
]Publisher severity
No explicit severity was provided.
- Event
- #57759 · Revision 1
- Added to Heist Feed
- Publisher date