Use After Free Affecting c-ares package, versions [,1.34.8)
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- published9 Jul 2026
- disclosed7 Jul 2026
- creditUnknown
Introduced: 7 Jul 2026
CVE-2026-33630 (opens in a new tab)How to fix?
Upgrade c-ares to version 1.34.8 or higher.
Overview
Affected versions of this package are vulnerable to Use After Free in the query completion process. An attacker can cause memory corruption and application crash by sending crafted DNS responses that manipulate the sequence of query completions, such as forcing an EDNS-downgrade retry and a connection reset, leading to access of freed memory. This is only exploitable if a malicious or on-path DNS server can interact with the client and force it to use TCP by setting the truncation (TC) bit in a UDP response.
Workaround
This vulnerability can be mitigated by using trusted DNS resolvers over a trusted transport (e.g., DNS-over-TLS) and avoiding calls to ares_cancel() from within a query callback.