UBUNTU-CVE-2026-55991
- Source
- https://ubuntu.com/security/CVE-2026-55991
- Import Source
- https://github.com/canonical/ubuntu-security-notices/blob/main/osv/cve/2026/UBUNTU-CVE-2026-55991.json
- JSON Data
- https://api.osv.dev/v1/vulns/UBUNTU-CVE-2026-55991
- Upstream
- Published
- 2026-07-22T14:17:00Z
- Modified
- 2026-08-20T23:26:27Z
- Severity
-
- 5.9 (Medium) CVSS_V3 - CVSS:3.1/AV:N/AC:H/PR:N/UI:N/S:U/C:N/I:N/A:H CVSS Calculator
- Ubuntu - medium
- Summary
- [none]
- Details
-
In NLnet Labs Unbound 1.22.0 up to and including 1.25.1, a remote unauthenticated client can trigger a libngtcp2 assertion (if compiled with assertions on) and terminate the entire Unbound process using a single DNS-over-QUIC (DoQ) connection and one normal DNS query. This is caused by an erroneous error value passed to libngtcp2. When 'ngtcp2_conn_writev_stream()' returns 'NGTCP2_ERR_STREAM_DATA_BLOCKED', Unbound continues to call 'ngtcp2_ccerr_set_application_error()' with a '-1' error value. The 'int' literal '-1' is implicitly converted to the function's 'uint64_t error_code' parameter as '0xFFFFFFFFFFFFFFFF'. The follow-on 'ngtcp2_conn_write_connection_close()' serialises that value as a QUIC variable-length integer; because '2^64-1' exceeds the 62-bit varint ceiling, 'ngtcp2_put_uvarintlen()' fails 'assert(n < 4611686018427387904ULL)' and the whole resolver process aborts. A remote, unauthenticated DoQ client can trigger this deterministically with a single QUIC connection by advertising 'initial_max_stream_data_bidi_local = 1' in its transport parameters and sending one DoQ query without ever reading the stream.
- References
Affected packages
Ubuntu:22.04:LTS
unbound
Package
- Name
- unbound
- Purl
- pkg:deb/ubuntu/unbound?arch=source&distro=jammy
Affected ranges
- Type
- ECOSYSTEM
- Events
-
Introduced0 Unknown introduced version / All previous versions are affected
Affected versions
1.*
1.13.1-1ubuntu1
1.13.1-1ubuntu3
1.13.1-1ubuntu5
1.13.1-1ubuntu5.1
1.13.1-1ubuntu5.2
1.13.1-1ubuntu5.3
1.13.1-1ubuntu5.4
1.13.1-1ubuntu5.5
1.13.1-1ubuntu5.7
1.13.1-1ubuntu5.8
1.13.1-1ubuntu5.10
1.13.1-1ubuntu5.11
1.13.1-1ubuntu5.12
1.13.1-1ubuntu5.13
1.13.1-1ubuntu5.14
1.13.1-1ubuntu5.15
Ecosystem specific
{
"binaries": [
{
"binary_name": "libunbound8",
"binary_version": "1.13.1-1ubuntu5.15"
},
{
"binary_name": "python3-unbound",
"binary_version": "1.13.1-1ubuntu5.15"
},
{
"binary_name": "unbound",
"binary_version": "1.13.1-1ubuntu5.15"
},
{
"binary_name": "unbound-anchor",
"binary_version": "1.13.1-1ubuntu5.15"
},
{
"binary_name": "unbound-host",
"binary_version": "1.13.1-1ubuntu5.15"
}
]
}Ubuntu:24.04:LTS
unbound
Package
- Name
- unbound
- Purl
- pkg:deb/ubuntu/unbound?arch=source&distro=noble
Affected ranges
- Type
- ECOSYSTEM
- Events
-
Introduced0 Unknown introduced version / All previous versions are affected
Affected versions
1.*
1.17.1-2
1.18.0-2ubuntu1
1.18.0-2ubuntu2
1.19.1-1ubuntu1
1.19.2-1ubuntu1
1.19.2-1ubuntu3
1.19.2-1ubuntu3.1
1.19.2-1ubuntu3.2
1.19.2-1ubuntu3.3
1.19.2-1ubuntu3.4
1.19.2-1ubuntu3.5
1.19.2-1ubuntu3.6
1.19.2-1ubuntu3.7
1.19.2-1ubuntu3.8
1.19.2-1ubuntu3.9
Ecosystem specific
{
"binaries": [
{
"binary_name": "libunbound8",
"binary_version": "1.19.2-1ubuntu3.9"
},
{
"binary_name": "python3-unbound",
"binary_version": "1.19.2-1ubuntu3.9"
},
{
"binary_name": "unbound",
"binary_version": "1.19.2-1ubuntu3.9"
},
{
"binary_name": "unbound-anchor",
"binary_version": "1.19.2-1ubuntu3.9"
},
{
"binary_name": "unbound-host",
"binary_version": "1.19.2-1ubuntu3.9"
}
]
}Ubuntu:26.04:LTS
unbound
Package
- Name
- unbound
- Purl
- pkg:deb/ubuntu/unbound?arch=source&distro=resolute
Affected ranges
- Type
- ECOSYSTEM
- Events
-
Introduced0 Unknown introduced version / All previous versions are affected
Affected versions
1.*
1.22.0-2ubuntu2
1.22.0-2ubuntu4
1.24.2-1ubuntu1
1.24.2-1ubuntu2
1.24.2-1ubuntu2.1
1.24.2-1ubuntu2.2
Ecosystem specific
{
"binaries": [
{
"binary_name": "libunbound8",
"binary_version": "1.24.2-1ubuntu2.2"
},
{
"binary_name": "python3-unbound",
"binary_version": "1.24.2-1ubuntu2.2"
},
{
"binary_name": "unbound",
"binary_version": "1.24.2-1ubuntu2.2"
},
{
"binary_name": "unbound-anchor",
"binary_version": "1.24.2-1ubuntu2.2"
},
{
"binary_name": "unbound-host",
"binary_version": "1.24.2-1ubuntu2.2"
}
]
}Ubuntu:Pro:14.04:LTS
unbound
Package
- Name
- unbound
- Purl
- pkg:deb/ubuntu/unbound?arch=source&distro=esm-infra-legacy%2Ftrusty
Affected ranges
- Type
- ECOSYSTEM
- Events
-
Introduced0 Unknown introduced version / All previous versions are affected
Affected versions
1.*
1.4.20-1
1.4.21-1
1.4.21-1ubuntu1
1.4.21-1ubuntu2
1.4.22-1ubuntu1
1.4.22-1ubuntu2
1.4.22-1ubuntu3
1.4.22-1ubuntu4
1.4.22-1ubuntu4.14.04.1
1.4.22-1ubuntu4.14.04.2
1.4.22-1ubuntu4.14.04.3
1.4.22-1ubuntu4.14.04.3+esm1
1.4.22-1ubuntu4.14.04.3+esm2
1.4.22-1ubuntu4.14.04.3+esm3
Ecosystem specific
{
"binaries": [
{
"binary_name": "libunbound2",
"binary_version": "1.4.22-1ubuntu4.14.04.3+esm3"
},
{
"binary_name": "python-unbound",
"binary_version": "1.4.22-1ubuntu4.14.04.3+esm3"
},
{
"binary_name": "unbound",
"binary_version": "1.4.22-1ubuntu4.14.04.3+esm3"
},
{
"binary_name": "unbound-anchor",
"binary_version": "1.4.22-1ubuntu4.14.04.3+esm3"
},
{
"binary_name": "unbound-host",
"binary_version": "1.4.22-1ubuntu4.14.04.3+esm3"
}
]
}Ubuntu:Pro:16.04:LTS
unbound
Package
- Name
- unbound
- Purl
- pkg:deb/ubuntu/unbound?arch=source&distro=esm-infra-legacy%2Fxenial
Affected ranges
- Type
- ECOSYSTEM
- Events
-
Introduced0 Unknown introduced version / All previous versions are affected
Affected versions
1.*
1.4.22-1ubuntu6
1.5.7-1ubuntu1
1.5.7-1ubuntu2
1.5.8-1ubuntu1
1.5.8-1ubuntu1.1
1.5.8-1ubuntu1.1+esm1
1.5.8-1ubuntu1.1+esm2
1.5.8-1ubuntu1.1+esm3
Ecosystem specific
{
"binaries": [
{
"binary_name": "libunbound2",
"binary_version": "1.5.8-1ubuntu1.1+esm3"
},
{
"binary_name": "python-unbound",
"binary_version": "1.5.8-1ubuntu1.1+esm3"
},
{
"binary_name": "unbound",
"binary_version": "1.5.8-1ubuntu1.1+esm3"
},
{
"binary_name": "unbound-anchor",
"binary_version": "1.5.8-1ubuntu1.1+esm3"
},
{
"binary_name": "unbound-host",
"binary_version": "1.5.8-1ubuntu1.1+esm3"
}
]
}Ubuntu:Pro:18.04:LTS
unbound
Package
- Name
- unbound
- Purl
- pkg:deb/ubuntu/unbound?arch=source&distro=esm-infra%2Fbionic
Affected ranges
- Type
- ECOSYSTEM
- Events
-
Introduced0 Unknown introduced version / All previous versions are affected
Affected versions
1.*
1.6.5-1
1.6.7-1
1.6.7-1build1
1.6.7-1ubuntu1
1.6.7-1ubuntu2
1.6.7-1ubuntu2.1
1.6.7-1ubuntu2.2
1.6.7-1ubuntu2.3
1.6.7-1ubuntu2.4
1.6.7-1ubuntu2.5
1.6.7-1ubuntu2.6
1.6.7-1ubuntu2.6+esm2
1.6.7-1ubuntu2.6+esm3
1.6.7-1ubuntu2.6+esm4
Ecosystem specific
{
"binaries": [
{
"binary_name": "libunbound2",
"binary_version": "1.6.7-1ubuntu2.6+esm4"
},
{
"binary_name": "python-unbound",
"binary_version": "1.6.7-1ubuntu2.6+esm4"
},
{
"binary_name": "python3-unbound",
"binary_version": "1.6.7-1ubuntu2.6+esm4"
},
{
"binary_name": "unbound",
"binary_version": "1.6.7-1ubuntu2.6+esm4"
},
{
"binary_name": "unbound-anchor",
"binary_version": "1.6.7-1ubuntu2.6+esm4"
},
{
"binary_name": "unbound-host",
"binary_version": "1.6.7-1ubuntu2.6+esm4"
}
]
}Ubuntu:Pro:20.04:LTS
unbound
Package
- Name
- unbound
- Purl
- pkg:deb/ubuntu/unbound?arch=source&distro=esm-infra%2Ffocal
Affected ranges
- Type
- ECOSYSTEM
- Events
-
Introduced0 Unknown introduced version / All previous versions are affected
Affected versions
1.*
1.9.0-2ubuntu1
1.9.0-2ubuntu2
1.9.4-2
1.9.4-2ubuntu1
1.9.4-2ubuntu1.1
1.9.4-2ubuntu1.2
1.9.4-2ubuntu1.3
1.9.4-2ubuntu1.4
1.9.4-2ubuntu1.5
1.9.4-2ubuntu1.6
1.9.4-2ubuntu1.8
1.9.4-2ubuntu1.9
1.9.4-2ubuntu1.11
1.9.4-2ubuntu1.11+esm1
Ecosystem specific
{
"binaries": [
{
"binary_name": "libunbound8",
"binary_version": "1.9.4-2ubuntu1.11+esm1"
},
{
"binary_name": "python-unbound",
"binary_version": "1.9.4-2ubuntu1.11+esm1"
},
{
"binary_name": "python3-unbound",
"binary_version": "1.9.4-2ubuntu1.11+esm1"
},
{
"binary_name": "unbound",
"binary_version": "1.9.4-2ubuntu1.11+esm1"
},
{
"binary_name": "unbound-anchor",
"binary_version": "1.9.4-2ubuntu1.11+esm1"
},
{
"binary_name": "unbound-host",
"binary_version": "1.9.4-2ubuntu1.11+esm1"
}
]
}