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.
Attack Parameters
Attack Vector
Network
Can be exploited remotely
Attack Complexity
Low
Easy to exploit
Privileges Required
None
No privileges needed
User Interaction
None
No user interaction needed
Impact Assessment
Confidentiality
None
No data leak
Integrity
None
No data modification
Availability
High
Complete denial of service
CVSS Vector v3.1
Weakness Type (CWE)
References 6
https://github.com/c-ares/c-ares/commit/5c8341ba6ff3a8e4e4dfd616f8ed0418838b8b7b
security-advisories@github.com
https://github.com/c-ares/c-ares/commit/f1288bbc70e9a1e0a77134c2382157e52d326aea
security-advisories@github.com
https://github.com/c-ares/c-ares/pull/1164
security-advisories@github.com
https://github.com/c-ares/c-ares/pull/1210
security-advisories@github.com
https://github.com/c-ares/c-ares/releases/tag/v1.34.7
security-advisories@github.com
https://github.com/c-ares/c-ares/security/advisories/GHSA-pjmc-gx33-gc76
security-advisories@github.com