Race condition in Unbound - CVE-2026-77955
Published: September 16, 2026 / Updated: September 19, 2026
Vulnerability identifier: #VU150189
CSH Severity: Low
CVSS v4: 6.3 [CVSS:4.0/AV:N/AC:L/AT:P/PR:N/UI:N/VC:N/VI:L/VA:N/SC:N/SI:N/SA:N]
CVE-ID: CVE-2026-77955
CWE-ID: CWE-362
Exploitation vector: Remote access
Exploit availability:
No public exploit available
Vulnerability details
The vulnerability allows a remote attacker to cause tampered zone contents to be served or stored on disk.
The vulnerability exists due to a race condition caused by asynchronous DS/DNSKEY resolution in ZONEMD validation for configured zones when validating ZONEMD-configured zones located below, but not at, a trust anchor. A remote attacker can exploit the validation window to cause tampered zone contents to become available before integrity verification completes.
When zonefile writing is enabled, data from a failed verification can persist on disk and be reloaded after restart until verification concludes again.
Affected software
Unbound
Fedora
unbound
Fedora
unbound
How to mitigate CVE-2026-77955
Install security update from vendor's website.
Unbound - update to 1.26.1
unbound - addressed in versions 1.26.1-1.fc43, 1.26.1-1.fc44, 1.26.1-1.fc45
unbound - addressed in versions 1.26.1-1.fc43, 1.26.1-1.fc44, 1.26.1-1.fc45