Harden DNS response parser against malformed replies#14
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The POSIX resolver parsed res_nquery() responses without validating record boundaries, trusting attacker-controlled header counts and RDLENGTH fields. A spoofed or malicious DNS reply could trigger out-of-bounds reads of the 64 KiB response buffer, causing crashes or leaking adjacent stack memory into the resolved addresses. - Bounds-check the fixed RR fields (TYPE/CLASS/TTL/RDLENGTH) and the question section before reading them. - Verify RDLENGTH stays within the response before use. - Guard the MX PREFERENCE subtraction against RDLENGTH < 2, which previously underflowed the unsigned length and advanced the cursor far past the buffer. - Require A/AAAA rdata to be large enough before inet_ntop() reads its fixed 4/16 bytes. - Advance the record cursor by the original RDLENGTH via a separate rdata pointer, decoupling it from the MX preference read. Co-Authored-By: Claude Opus 4.8 (1M context) <noreply@anthropic.com>
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The POSIX resolver parsed
res_nquery()responses without validating record boundaries, trusting attacker-controlled header counts and RDLENGTH fields. A spoofed or malicious DNS reply could trigger out-of-bounds reads of the 64 KiB response buffer, causing crashes or leaking adjacent stack memory into the resolved addresses.inet_ntop()reads its fixed 4/16 bytes.