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CVE-2026-55717 on CTRL-OS 26.05

Aliases: CVE-2026-55717

Packages: unbound

Status: In Progress

Advisory Information

In NLnet Labs Unbound 1.10.0 up to and including 1.25.1, when 'serve-expired: yes' is set together with a 'response-ip: redirect' /'response-ip-data: CNAME ' rule (or the RPZ 'rpz-cname-override' equivalent), a remote client who controls any delegated domain can crash the daemon. The serve-expired-client-timeout callback runs a two-pass loop to chase the respip-generated CNAME alias; on the second pass it resets 'alias_rrset' but not 'partial_rep'. Later, this inconsistency leads to a NULL pointer dereference and an eventual crash. A malicious actor can exploit the vulnerability by controlling any zone that replies with an A/AAAA record that falls inside the configured response-ip/rpz subnet. By delaying the answer when the previous record has expired, the vulnerable path of 'serve-expired-client-timeout' is taken leading to denial of service via the server crash.

Updates

2026-07-27 19:41 CEST

Metadata changes:

  • Status for package unbound: “In Progress” (6adb4107d901bc4e75e7e4659d2eccdaebe38c21)

2026-07-23 23:53 CEST

Metadata changes:

  • Status for package unbound: “Plausible”

2026-07-23 23:53 CEST

Metadata changes:

  • Status for package unbound: “New”