CVE catalog
CVE-2026-55973
In NLnet Labs Unbound 1.23.0 up to and including 1.25.1, when 'dns-error-reporting: yes' is set, the EDNS Report-Channel option (code 18) from the last upstream response is read and uses the option's
- Severity
- High · CVSS 7.5
CVSS:3.1/AV:N/AC:L/PR:N/UI:N/S:U/C:N/I:N/A:H - Published
- Source
- [NVD] · [CVE record]
- EPSS
- 0.28% · Oct 25, 2026
In NLnet Labs Unbound 1.23.0 up to and including 1.25.1, when 'dns-error-reporting: yes' is set, the EDNS Report-Channel option (code 18) from the last upstream response is read and uses the option's length as the length of the agent domain. When a domain name check is performed on the agent domain, the returned lenght is not used and if the agent domain is followed by garbage, those bytes are moved onto the tail of the synthetic '_er.' report query name. That query name is later used in the iterator via a subquery to send out the DNS Error Report and when Unbound tries to walk that query name during 'find_closest_of_type()', it strips labels using the query name length rather than stopping at the embedded root, walks one byte past it, and feeds the first garbage byte to 'dname_query_hash()' as a label length writing over the stack variable 'labuf'. One ordinary upstream response from a delegated zone the attacker controls is sufficient to terminate the daemon.
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 | 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-2026-55973 | Not reported |
| Alpine | unbound | apk | 3.23 | 1.25.2-r0 | Not reported | ALPINE-CVE-2026-55973 | Not reported |
| Alpine | unbound | apk | 3.24 | 1.25.2-r0 | Not reported | ALPINE-CVE-2026-55973 | Not reported |
| Ubuntu | unbound | deb | 26.04 | 1.24.2-1ubuntu2.4 | Not reported | UBUNTU-CVE-2026-55973 | Not reported |
| Cpe | unbound | cpe | Not reported | 1.25.2 | Not reported | NVD-CVE-2026-55973 | Not reported |
OpenFactory catalog packages
[Debian 12 (Bookworm)]
- [libunbound8]Affected
Source package: [unbound]
Details (4)
1.17.1-2+deb12u4· amd64 · bookwormAffected
nvd · unbound · debian · bookworm; nvd · unbound · debian · 12
1.17.1-2+deb12u4· arm64 · bookwormAffected
nvd · unbound · debian · bookworm; nvd · unbound · debian · 12
1.17.1-2+deb12u3· amd64 · bookworm-securityAffected
nvd · unbound · debian · bookworm; nvd · unbound · debian · 12
1.17.1-2+deb12u3· arm64 · bookworm-securityAffected
nvd · unbound · debian · bookworm; nvd · unbound · debian · 12
- [libunbound-dev]Affected
Source package: [unbound]
Details (4)
1.17.1-2+deb12u4· amd64 · bookwormAffected
nvd · unbound · debian · bookworm; nvd · unbound · debian · 12
1.17.1-2+deb12u4· arm64 · bookwormAffected
nvd · unbound · debian · bookworm; nvd · unbound · debian · 12
1.17.1-2+deb12u3· amd64 · bookworm-securityAffected
nvd · unbound · debian · bookworm; nvd · unbound · debian · 12
1.17.1-2+deb12u3· arm64 · bookworm-securityAffected
nvd · unbound · debian · bookworm; nvd · unbound · debian · 12
- [python3-unbound]Affected
Source package: [unbound]
Details (4)
1.17.1-2+deb12u4· amd64 · bookwormAffected
nvd · unbound · debian · bookworm; nvd · unbound · debian · 12
1.17.1-2+deb12u4· arm64 · bookwormAffected
nvd · unbound · debian · bookworm; nvd · unbound · debian · 12
1.17.1-2+deb12u3· amd64 · bookworm-securityAffected
nvd · unbound · debian · bookworm; nvd · unbound · debian · 12
1.17.1-2+deb12u3· arm64 · bookworm-securityAffected
nvd · unbound · debian · bookworm; nvd · unbound · debian · 12
- [unbound]Affected
Details (4)
1.17.1-2+deb12u4· amd64 · bookwormAffected
nvd · unbound · debian · bookworm; nvd · unbound · debian · 12
1.17.1-2+deb12u4· arm64 · bookwormAffected
nvd · unbound · debian · bookworm; nvd · unbound · debian · 12
1.17.1-2+deb12u3· amd64 · bookworm-securityAffected
nvd · unbound · debian · bookworm; nvd · unbound · debian · 12
1.17.1-2+deb12u3· arm64 · bookworm-securityAffected
nvd · unbound · debian · bookworm; nvd · unbound · debian · 12
- [unbound-anchor]Affected
Source package: [unbound]
Details (4)
1.17.1-2+deb12u4· amd64 · bookwormAffected
nvd · unbound · debian · bookworm; nvd · unbound · debian · 12
1.17.1-2+deb12u4· arm64 · bookwormAffected
nvd · unbound · debian · bookworm; nvd · unbound · debian · 12
1.17.1-2+deb12u3· amd64 · bookworm-securityAffected
nvd · unbound · debian · bookworm; nvd · unbound · debian · 12
1.17.1-2+deb12u3· arm64 · bookworm-securityAffected
nvd · unbound · debian · bookworm; nvd · unbound · debian · 12
- [unbound-host]Affected
Source package: [unbound]
Details (4)
1.17.1-2+deb12u4· amd64 · bookwormAffected
nvd · unbound · debian · bookworm; nvd · unbound · debian · 12
1.17.1-2+deb12u4· arm64 · bookwormAffected
nvd · unbound · debian · bookworm; nvd · unbound · debian · 12
1.17.1-2+deb12u3· amd64 · bookworm-securityAffected
nvd · unbound · debian · bookworm; nvd · unbound · debian · 12
1.17.1-2+deb12u3· arm64 · bookworm-securityAffected
nvd · unbound · debian · bookworm; nvd · unbound · debian · 12
[Debian 13 (Trixie)]
- [libunbound8]Affected
Source package: [unbound]
Details (6)
1.22.0-2+deb13u3· amd64 · trixieAffected · Fixed:
1.26.1-0+deb13u1nvd · unbound · debian · 13
1.22.0-2+deb13u3· arm64 · trixieAffected · Fixed:
1.26.1-0+deb13u1nvd · unbound · debian · 13
1.22.0-2+deb13u3· amd64 · trixie-security · Historical versionAffected · Fixed:
1.26.1-0+deb13u1nvd · unbound · debian · 13
1.22.0-2+deb13u3· arm64 · trixie-securityAffected · Fixed:
1.26.1-0+deb13u1nvd · unbound · debian · 13
1.26.1-0+deb13u1· amd64 · trixie-security · Historical versionFixed · Fixed:
1.26.1-0+deb13u1nvd · unbound · debian · 13
1.26.2-0+deb13u1· amd64 · trixie-securityFixed · Fixed:
1.26.1-0+deb13u1nvd · unbound · debian · 13
- [libunbound-dev]Affected
Source package: [unbound]
Details (6)
1.22.0-2+deb13u3· amd64 · trixieAffected · Fixed:
1.26.1-0+deb13u1nvd · unbound · debian · 13
1.22.0-2+deb13u3· arm64 · trixieAffected · Fixed:
1.26.1-0+deb13u1nvd · unbound · debian · 13
1.22.0-2+deb13u3· amd64 · trixie-security · Historical versionAffected · Fixed:
1.26.1-0+deb13u1nvd · unbound · debian · 13
1.22.0-2+deb13u3· arm64 · trixie-securityAffected · Fixed:
1.26.1-0+deb13u1nvd · unbound · debian · 13
1.26.1-0+deb13u1· amd64 · trixie-security · Historical versionFixed · Fixed:
1.26.1-0+deb13u1nvd · unbound · debian · 13
1.26.2-0+deb13u1· amd64 · trixie-securityFixed · Fixed:
1.26.1-0+deb13u1nvd · unbound · debian · 13
- [python3-unbound]Affected
Source package: [unbound]
Details (6)
1.22.0-2+deb13u3· amd64 · trixieAffected · Fixed:
1.26.1-0+deb13u1nvd · unbound · debian · 13
1.22.0-2+deb13u3· arm64 · trixieAffected · Fixed:
1.26.1-0+deb13u1nvd · unbound · debian · 13
1.22.0-2+deb13u3· amd64 · trixie-security · Historical versionAffected · Fixed:
1.26.1-0+deb13u1nvd · unbound · debian · 13
1.22.0-2+deb13u3· arm64 · trixie-securityAffected · Fixed:
1.26.1-0+deb13u1nvd · unbound · debian · 13
1.26.1-0+deb13u1· amd64 · trixie-security · Historical versionFixed · Fixed:
1.26.1-0+deb13u1nvd · unbound · debian · 13
1.26.2-0+deb13u1· amd64 · trixie-securityFixed · Fixed:
1.26.1-0+deb13u1nvd · unbound · debian · 13
- [unbound]Affected
Details (6)
1.22.0-2+deb13u3· amd64 · trixieAffected · Fixed:
1.26.1-0+deb13u1nvd · unbound · debian · 13
1.22.0-2+deb13u3· arm64 · trixieAffected · Fixed:
1.26.1-0+deb13u1nvd · unbound · debian · 13
1.22.0-2+deb13u3· amd64 · trixie-security · Historical versionAffected · Fixed:
1.26.1-0+deb13u1nvd · unbound · debian · 13
1.22.0-2+deb13u3· arm64 · trixie-securityAffected · Fixed:
1.26.1-0+deb13u1nvd · unbound · debian · 13
1.26.1-0+deb13u1· amd64 · trixie-security · Historical versionFixed · Fixed:
1.26.1-0+deb13u1nvd · unbound · debian · 13
1.26.2-0+deb13u1· amd64 · trixie-securityFixed · Fixed:
1.26.1-0+deb13u1nvd · unbound · debian · 13
- [unbound-anchor]Affected
Source package: [unbound]
Details (6)
1.22.0-2+deb13u3· amd64 · trixieAffected · Fixed:
1.26.1-0+deb13u1nvd · unbound · debian · 13
1.22.0-2+deb13u3· arm64 · trixieAffected · Fixed:
1.26.1-0+deb13u1nvd · unbound · debian · 13
1.22.0-2+deb13u3· amd64 · trixie-security · Historical versionAffected · Fixed:
1.26.1-0+deb13u1nvd · unbound · debian · 13
1.22.0-2+deb13u3· arm64 · trixie-securityAffected · Fixed:
1.26.1-0+deb13u1nvd · unbound · debian · 13
1.26.1-0+deb13u1· amd64 · trixie-security · Historical versionFixed · Fixed:
1.26.1-0+deb13u1nvd · unbound · debian · 13
1.26.2-0+deb13u1· amd64 · trixie-securityFixed · Fixed:
1.26.1-0+deb13u1nvd · unbound · debian · 13
- [unbound-host]Affected
Source package: [unbound]
Details (6)
1.22.0-2+deb13u3· amd64 · trixieAffected · Fixed:
1.26.1-0+deb13u1nvd · unbound · debian · 13
1.22.0-2+deb13u3· arm64 · trixieAffected · Fixed:
1.26.1-0+deb13u1nvd · unbound · debian · 13
1.22.0-2+deb13u3· amd64 · trixie-security · Historical versionAffected · Fixed:
1.26.1-0+deb13u1nvd · unbound · debian · 13
1.22.0-2+deb13u3· arm64 · trixie-securityAffected · Fixed:
1.26.1-0+deb13u1nvd · unbound · debian · 13
1.26.1-0+deb13u1· amd64 · trixie-security · Historical versionFixed · Fixed:
1.26.1-0+deb13u1nvd · unbound · debian · 13
1.26.2-0+deb13u1· amd64 · trixie-securityFixed · Fixed:
1.26.1-0+deb13u1nvd · unbound · debian · 13
Observed:
References
- [https://ftp.suse.com/pub/projects/security/csaf/opensuse-su-2026_11380-1.json]
- [https://nvd.nist.gov/vuln/detail/CVE-2026-55973]
- [https://osv.dev/vulnerability/ALPINE-CVE-2026-55973]
- [https://osv.dev/vulnerability/DEBIAN-CVE-2026-55973]
- [https://osv.dev/vulnerability/UBUNTU-CVE-2026-55973]
- [https://security-tracker.debian.org/tracker/CVE-2026-55973]
- [https://security.access.redhat.com/data/csaf/v2/vex/2026/cve-2026-55973.json]
- [https://wid.cert-bund.de/.well-known/csaf/white/2026/wid-sec-w-2026-3038.json]
- [https://www.nlnetlabs.nl/downloads/unbound/CVE-2026-55973.txt]
[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]