CVE-2026-40691

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Source
https://cve.org/CVERecord?id=CVE-2026-40691
Import Source
https://storage.googleapis.com/cve-osv-conversion/osv-output/CVE-2026-40691.json
JSON Data
https://api.osv.dev/v1/vulns/CVE-2026-40691
Downstream
Related
Published
2026-07-22T14:17:18.437Z
Modified
2026-07-27T14:06:41.503499Z
Severity
  • 7.5 (High) CVSS_V3 - CVSS:3.1/AV:N/AC:L/PR:N/UI:N/S:U/C:N/I:N/A:H CVSS Calculator
Summary
[none]
Details

In Unbound 1.9.0 up to and including 1.25.1, when a DNSCrypt query is received over TCP, the routine that encrypts the reply in place fails to bound the reply length against the destination buffer size. The size clamp that protects the UDP path is not applied on the TCP path, so a reply larger than 65504 bytes is shifted forward by 48 bytes inside a buffer of capacity equal to 'msg-buffer-size', writing past the end of the heap allocation. A single malicious encrypted query crashes the resolver and lead to denial of service. This vulnerability needs Unbound to be compiled with DNSCrypt support ('--enable-dnscrypt') and the 'dnscrypt:' clause to be configured and enabled for the listening interfaces.

References

Affected packages

Git / github.com/nlnetlabs/unbound

Affected ranges

Type
GIT
Repo
https://github.com/nlnetlabs/unbound
Events
Introduced
29a0405c6c618f11328b5d74904e78f65ea636b6
Fixed
c33ad1b1a21e48bfe4f140e90252a9be1b0c5745
Database specific 
{
    "cpe": "cpe:2.3:a:nlnetlabs:unbound:*:*:*:*:*:*:*:*",
    "extracted_events": [
        {
            "introduced": "1.9.0"
        },
        {
            "fixed": "1.25.2"
        }
    ],
    "source": "CPE_RANGE"
}

Database specific

source 
"https://storage.googleapis.com/cve-osv-conversion/osv-output/CVE-2026-40691.json"