CVE-2026-82720: Use-after-free in DoH stream cleanup code path
NLnet Labs Unbound 1.12.0 up to and including 1.26.0 has a use-after-free vulnerability when compiled for DNS-over-HTTPs support with '--with-libnghttp2'. During failure code paths (i.e., RPZ drop query, jostle due to heavy traffic), a dropped DoH stream brings down the whole DoH session and does not account properly for other DoH streams in the same session. This leads to use-after-free in those code paths. If the prerequisites are satisfied (possible RPZ drop or heavy client traffic), a malicious actor can trigger the vulnerability with a single DoH connection and the appropriate traffic. Impact is limited as the reads are not user controlled and the use-after-free leads to early returns. However, a hardened allocator can catch the use-after-free and controllably terminate the process resulting to denial of service.
Affected Software
Remediation
Recommended actions to resolve this vulnerability, in priority order.
- Upgrade
Upgrade
NLnet Labs Unboundto a version that resolves this vulnerability.Fixed in 1.26.1
Event History
Frequently Asked Questions
Which deployments are exposed?
Unbound versions 1.12.0 through 1.26.0 are affected only when built with DNS-over-HTTPS support using '--with-libnghttp2'. The vulnerable path requires DoH traffic.
What conditions are needed to trigger the issue?
An attacker can use a single DoH connection with appropriate traffic, but a failure path must occur: either an RPZ drop query or jostling caused by heavy client traffic. No attacker privileges or user interaction are required.
What is the practical impact?
The issue can result in denial of service if a hardened allocator detects the use-after-free and terminates the Unbound process. The reads are not user-controlled and lead to early returns, which limits the stated impact.