CVE-2023-31137: Debian Linux

High severity, CVSS 7.5. EPSS: 1.1% chance of exploitation in the next 30 days.

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.

Affected products

• Debian Debian Linux: version 10.0 only; version 11.0 only
• Fedoraproject Fedora: version 37 only; version 38 only
• Maradns Maradns: before 3.4.10 (fixed in 3.4.10); from 3.5.0001, before 3.5.0036 (fixed in 3.5.0036)

Published 2023-05-09. Last modified 2026-06-17.