CVE-2023-31137

Date: May 9, 2023

MaraDNS is open-source software that implements the Domain Name System (DNS). In version 3.5.0024 and prior, a remotely exploitable integer underflow vulnerability in the DNS packet decompression function allows an attacker to cause a Denial of Service by triggering an abnormal program termination. The vulnerability exists in the "decomp_get_rddata" function within the "Decompress.c" file. When handling a DNS packet with an Answer RR of qtype 16 (TXT record) and any qclass, if the "rdlength" is smaller than "rdata", the result of the line "Decompress.c:886" is a negative number "len = rdlength - total;". This value is then passed to the "decomp_append_bytes" function without proper validation, causing the program to attempt to allocate a massive chunk of memory that is impossible to allocate. Consequently, the program exits with an error code of 64, causing a Denial of Service. One proposed fix for this vulnerability is to patch "Decompress.c:887" by breaking "if(len <= 0)", which has been incorporated in version 3.5.0036 via commit bab062bde40b2ae8a91eecd522e84d8b993bab58.

Language: C