CVE-2023-31137

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.