CVE-2026-50046 (Medium) detected in src4.0.4, src4.0.4 - autoclosed

[mend-bolt-for-github]

CVE-2026-50046 - Medium Severity Vulnerability

Vulnerable Libraries - src4.0.4, src4.0.4

src4.0.4

Library home page: https://github.com/MidnightBSD/src.git

Vulnerable Source Files (2)

/contrib/unbound/services/outside_network.h
/contrib/unbound/services/outside_network.c

src4.0.4

Library home page: https://github.com/MidnightBSD/src.git

Vulnerable Source Files (2)

/contrib/unbound/services/outside_network.h
/contrib/unbound/services/outside_network.c

Found in HEAD commit: 816463d989cc5839c1cca2efb5bf2503408507fb

Found in base branches: stable/4.0, master

Vulnerability Details

In NLnet Labs Unbound 1.15.0 up to and including 1.25.1, the TLS server name used for DNS-over-TLS (DoT) forwarded queries is tied to a struct's ('serviced_query') lifetime but also referenced by another struct ('waiting_tcp'). When the owning struct is jostled out of the mesh while the DoT TCP stream is still handshaking it frees the storage behind the referenced string and if the TLS stream then errors out, it dereferences the freed pointer. The dereference is read-only and the practical impact is a daemon crash resulting in denial of service. A malicious actor that knows a DoT forwarding/stub Unbound's configuration could exploit the vulnerability by quering records in the appropriate zone while keeping Unbound uder pressure so that the jostle logic kicks in. If answers for the vulnerable zone are slow, the likelihood of jostling such queries is higher, although the timing of the jostle needs to be precise. Requirements for a vulnerable Unbound is the existence of a stub/forward zone configured for DoT together with a configured '#authname' suffix on the server identification. The connectivity to the server needs to exhibit a transient failure at the correct time in order to kick off the vulnerable error path.

Publish Date: 2026-07-22

URL: CVE-2026-50046

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

For more information on CVSS3 Scores, click here.

Suggested Fix

Type: Upgrade version

Release Date: 2026-07-22

Fix Resolution: https://github.com/NLnetLabs/unbound.git - release-1.25.2

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