unbound — security advisory
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.
- Products
- unbound
- Affected 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, 1.22.0-2+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, 1.26.1-1, 1.26.2-1
- Fixed versions
- 1.25.2-1, 1.26.1-0+deb13u1
- CVEs
- CVE-2026-55991
- Confirmed fixed CVEs
- Not specified
- Updated in this feed
- 1 Nov 2026, 09:57 UTC · Revision 2
Source evidence
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.
osv:DEBIAN-CVE-2026-55991
unbound
Fixed versions: Not specified
unbound
Fixed versions: 1.26.1-0+deb13u1
unbound
Fixed versions: 1.25.2-1
Complete source record
{
"id": "3ee2a41658cb3b09ee7bca6747a5ef8a2fdbff60da8cddd6a97820238bb781aa",
"url": "https://osv.dev/vulnerability/DEBIAN-CVE-2026-55991",
"method": "structured",
"payload": {
"kind": "advisory",
"title": "DEBIAN-CVE-2026-55991",
"summary": "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.",
"evidence": "osv:DEBIAN-CVE-2026-55991",
"products": [
{
"name": {
"value": "unbound",
"evidence": "/affected/0/package/name"
},
"prerequisites": [],
"fixed_versions": [],
"affected_versions": [
{
"value": "1.17.1-2",
"evidence": "/affected/0/versions"
},
{
"value": "1.17.1-2+deb12u1",
"evidence": "/affected/0/versions"
},
{
"value": "1.17.1-2+deb12u2",
"evidence": "/affected/0/versions"
},
{
"value": "1.17.1-2+deb12u3",
"evidence": "/affected/0/versions"
},
{
"value": "1.17.1-2+deb12u4",
"evidence": "/affected/0/versions"
},
{
"value": "1.17.1-2+loong64",
"evidence": "/affected/0/versions"
},
{
"value": "1.18.0-1",
"evidence": "/affected/0/versions"
},
{
"value": "1.18.0-2",
"evidence": "/affected/0/versions"
},
{
"value": "1.19.1-1",
"evidence": "/affected/0/versions"
},
{
"value": "1.19.2-1",
"evidence": "/affected/0/versions"
},
{
"value": "1.20.0-1",
"evidence": "/affected/0/versions"
},
{
"value": "1.21.1-1",
"evidence": "/affected/0/versions"
},
{
"value": "1.22.0-1",
"evidence": "/affected/0/versions"
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{
"value": "1.22.0-2",
"evidence": "/affected/0/versions"
},
{
"value": "1.23.1-1",
"evidence": "/affected/0/versions"
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{
"value": "1.24.0-1",
"evidence": "/affected/0/versions"
},
{
"value": "1.24.0-2",
"evidence": "/affected/0/versions"
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{
"value": "1.24.1-1",
"evidence": "/affected/0/versions"
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{
"value": "1.24.1-2",
"evidence": "/affected/0/versions"
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{
"value": "1.24.2-1",
"evidence": "/affected/0/versions"
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{
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"evidence": "/affected/0/versions"
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{
"value": "1.25.1-1",
"evidence": "/affected/0/versions"
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{
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"evidence": "/affected/0/versions"
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{
"value": "1.26.0-1",
"evidence": "/affected/0/versions"
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{
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"evidence": "/affected/0/versions"
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{
"value": "1.26.1-1",
"evidence": "/affected/0/versions"
},
{
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"evidence": "/affected/0/versions"
}
]
},
{
"name": {
"value": "unbound",
"evidence": "/affected/1/package/name"
},
"prerequisites": [],
"fixed_versions": [
{
"value": "1.26.1-0+deb13u1",
"evidence": "/affected/1/ranges"
}
],
"affected_versions": [
{
"value": "1.22.0-2",
"evidence": "/affected/1/versions"
},
{
"value": "1.22.0-2+deb13u1",
"evidence": "/affected/1/versions"
},
{
"value": "1.22.0-2+deb13u2",
"evidence": "/affected/1/versions"
},
{
"value": "1.22.0-2+deb13u3",
"evidence": "/affected/1/versions"
},
{
"value": "1.23.1-1",
"evidence": "/affected/1/versions"
},
{
"value": "1.24.0-1",
"evidence": "/affected/1/versions"
},
{
"value": "1.24.0-2",
"evidence": "/affected/1/versions"
},
{
"value": "1.24.1-1",
"evidence": "/affected/1/versions"
},
{
"value": "1.24.1-2",
"evidence": "/affected/1/versions"
},
{
"value": "1.24.2-1",
"evidence": "/affected/1/versions"
},
{
"value": "1.25.0-1",
"evidence": "/affected/1/versions"
},
{
"value": "1.25.1-1",
"evidence": "/affected/1/versions"
},
{
"value": "1.25.2-1",
"evidence": "/affected/1/versions"
},
{
"value": "1.26.0-1",
"evidence": "/affected/1/versions"
},
{
"value": "1.26.0-2",
"evidence": "/affected/1/versions"
}
]
},
{
"name": {
"value": "unbound",
"evidence": "/affected/2/package/name"
},
"prerequisites": [],
"fixed_versions": [
{
"value": "1.25.2-1",
"evidence": "/affected/2/ranges"
}
],
"affected_versions": [
{
"value": "1.22.0-2",
"evidence": "/affected/2/versions"
},
{
"value": "1.23.1-1",
"evidence": "/affected/2/versions"
},
{
"value": "1.24.0-1",
"evidence": "/affected/2/versions"
},
{
"value": "1.24.0-2",
"evidence": "/affected/2/versions"
},
{
"value": "1.24.1-1",
"evidence": "/affected/2/versions"
},
{
"value": "1.24.1-2",
"evidence": "/affected/2/versions"
},
{
"value": "1.24.2-1",
"evidence": "/affected/2/versions"
},
{
"value": "1.25.0-1",
"evidence": "/affected/2/versions"
},
{
"value": "1.25.1-1",
"evidence": "/affected/2/versions"
}
]
}
],
"severity": "medium",
"structured": {
"id": "DEBIAN-CVE-2026-55991",
"aliases": [
"DEBIAN-CVE-2026-55991"
],
"metrics": [
{
"type": "CVSS_V3",
"score": "CVSS:3.1/AV:N/AC:H/PR:N/UI:N/S:U/C:N/I:N/A:H"
}
],
"affected": [
{
"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-2026-55991.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-2026-55991.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-2026-55991.json"
},
"ecosystem_specific": {
"urgency": "not yet assigned"
}
}
],
"modified": "2026-10-25T10:00:57.992591470Z",
"provider": "osv",
"upstream": [
"CVE-2026-55991"
],
"references": [
"https://security-tracker.debian.org/tracker/CVE-2026-55991"
]
},
"related_cves": [
{
"value": "CVE-2026-55991",
"evidence": "/upstream"
}
],
"security_relevant": true,
"severity_evidence": "/severity/0/score"
},
"source_id": "core-osv",
"document_id": 445386,
"published_at": "2026-07-22T14:17:21.957+00:00"
}