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CVE-2026-55991 (Medium) detected in freebsd-srcrelease/15.0.0-p7 #475
Description
CVE-2026-55991 - Medium Severity Vulnerability
Vulnerable Library - freebsd-srcrelease/15.0.0-p7
The FreeBSD src tree publish-only repository. Experimenting with 'simple' pull requests....
Library home page: https://github.com/freebsd/freebsd-src.git
Found in base branches: stable/4.0, master
Vulnerable Source Files (1)
Vulnerability 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.
Publish Date: 2026-07-22
URL: CVE-2026-55991
CVSS 3 Score Details (5.9)
Base Score Metrics:
- Exploitability Metrics:
- Attack Vector: Network
- Attack Complexity: High
- Privileges Required: None
- User Interaction: None
- Scope: Unchanged
- Impact Metrics:
- Confidentiality Impact: None
- Integrity Impact: None
- Availability Impact: High
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Activity
[-]CVE-2026-55991 (Medium) detected in freebsd-srcrelease/15.0.0-p7[/-][+]CVE-2026-55991 (Medium) detected in src4.0.4[/+][-]CVE-2026-55991 (Medium) detected in src4.0.4[/-][+]CVE-2026-55991 (Medium) detected in freebsd-srcrelease/15.0.0-p7[/+][-]CVE-2026-55991 (Medium) detected in freebsd-srcrelease/15.0.0-p7[/-][+]CVE-2026-55991 (Medium) detected in src4.0.4[/+][-]CVE-2026-55991 (Medium) detected in src4.0.4[/-][+]CVE-2026-55991 (Medium) detected in freebsd-srcrelease/15.0.0-p7[/+][-]CVE-2026-55991 (Medium) detected in freebsd-srcrelease/15.0.0-p7[/-][+]CVE-2026-55991 (Medium) detected in src4.0.4[/+][-]CVE-2026-55991 (Medium) detected in src4.0.4[/-][+]CVE-2026-55991 (Medium) detected in freebsd-srcrelease/15.0.0-p7[/+][-]CVE-2026-55991 (Medium) detected in freebsd-srcrelease/15.0.0-p7[/-][+]CVE-2026-55991 (Medium) detected in src4.0.4[/+][-]CVE-2026-55991 (Medium) detected in src4.0.4[/-][+]CVE-2026-55991 (Medium) detected in freebsd-srcrelease/15.0.0-p7[/+][-]CVE-2026-55991 (Medium) detected in freebsd-srcrelease/15.0.0-p7[/-][+]CVE-2026-55991 (Medium) detected in src4.0.4[/+][-]CVE-2026-55991 (Medium) detected in src4.0.4[/-][+]CVE-2026-55991 (Medium) detected in freebsd-srcrelease/15.0.0-p7[/+][-]CVE-2026-55991 (Medium) detected in freebsd-srcrelease/15.0.0-p7[/-][+]CVE-2026-55991 (Medium) detected in src4.0.4[/+][-]CVE-2026-55991 (Medium) detected in src4.0.4[/-][+]CVE-2026-55991 (Medium) detected in freebsd-srcrelease/15.0.0-p7[/+][-]CVE-2026-55991 (Medium) detected in freebsd-srcrelease/15.0.0-p7[/-][+]CVE-2026-55991 (Medium) detected in src4.0.4[/+][-]CVE-2026-55991 (Medium) detected in src4.0.4[/-][+]CVE-2026-55991 (Medium) detected in freebsd-srcrelease/15.0.0-p7[/+][-]CVE-2026-55991 (Medium) detected in freebsd-srcrelease/15.0.0-p7[/-][+]CVE-2026-55991 (Medium) detected in src4.0.4[/+][-]CVE-2026-55991 (Medium) detected in src4.0.4[/-][+]CVE-2026-55991 (Medium) detected in freebsd-srcrelease/15.0.0-p7[/+][-]CVE-2026-55991 (Medium) detected in freebsd-srcrelease/15.0.0-p7[/-][+]CVE-2026-55991 (Medium) detected in src4.0.4[/+][-]CVE-2026-55991 (Medium) detected in src4.0.4[/-][+]CVE-2026-55991 (Medium) detected in src4.0.4 - autoclosed[/+]mend-bolt-for-github commentedon Sep 18, 2026
✔️ This issue was automatically closed by Mend because the vulnerable library in the specific branch(es) was either marked as ignored or it is no longer part of the Mend inventory.
[-]CVE-2026-55991 (Medium) detected in src4.0.4 - autoclosed[/-][+]CVE-2026-55991 (Medium) detected in freebsd-srcrelease/15.0.0-p7[/+]mend-bolt-for-github commentedon Oct 7, 2026
ℹ️ This issue was automatically re-opened by Mend because the vulnerable library in the specific branch(es) has been detected in the Mend inventory.