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c-ares is an asynchronous resolver library. Prior to 1.34.7, ares_dns_name_parse() enforces backward DNS compression pointers but does not bound the total pointer hops or assembled name length. A malicious DNS server can send a response containing a long descending pointer chain and many resource records whose NAME or RDATA fields refer to the chain, causing repeated decompression work that grows quadratically with message size. A single crafted response can stall the single-threaded c-ares event loop and deny DNS resolution, without causing memory corruption or information disclosure. This issue is fixed in version 1.34.7.
| Product | Vendor Advisory | Solution File | Added | Published |
|---|---|---|---|---|
| Ubuntu | — | Upgrade libc-ares2 (Ubuntu Pro)Upgrade libcares2Upgrade libc-ares2 | Oct 22, 2026 | Oct 21, 2026 |
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