Bug 2535057 (CVE-2026-85501) - CVE-2026-85501 unbound: Unbound: Denial of Service via algorithmic complexity attacks on DNSSEC
Summary: CVE-2026-85501 unbound: Unbound: Denial of Service via algorithmic complexity...
Keywords:
Status: NEW
Alias: CVE-2026-85501
Product: Security Response
Classification: Other
Component: vulnerability
Version: unspecified
Hardware: All
OS: Linux
medium
medium
Target Milestone: ---
Assignee: Product Security DevOps Team
QA Contact:
URL:
Whiteboard:
Depends On: 2537353
Blocks:
TreeView+ depends on / blocked
 
Reported: 2026-09-16 09:06 UTC by OSIDB Bzimport
Modified: 2026-09-21 10:15 UTC (History)
17 users (show)

Fixed In Version:
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Description OSIDB Bzimport 2026-09-16 09:06:52 UTC
Novel vulnerabilities to launch algorithmic complexity attacks on DNSSEC have been researched under the term 'ReTrap'. These result in degradation of service when malicious zones are used to serve the algorithmic complexity vulnerabilities. NLnet Labs Unbound up to and including 1.26.0 is vulnerable to some of them. TagTrap, where  the triple(Zone, Algo, KeyTag) matching mechanism introduces a significant attack vector when resolvers handle malicious responses containing numerous mismatched DNSKEY, RRSIG, and DS record. DelegationTrap, where constructing the chain-of-trust requires iterative validation of DNSKEY and DS records from the root zone downward. For deeply nested domains, this results in significant computational overhead. NsecTrap, where  responses with excessive invalid NSEC records compel the resolver to validate each one. AdditionalTrap, where Unbound by default would try to DNSSEC validate the ADDITIONAL section as well. This can be exploited to waste validation resources by malicious users.


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