The probability is the direct output of the EPSS model, and conveys an overall sense of the threat of exploitation in the wild. The percentile measures the EPSS probability relative to all known EPSS scores. Note: This data is updated daily, relying on the latest available EPSS model version. Check out the EPSS documentation for more details.
In a few clicks we can analyze your entire application and see what components are vulnerable in your application, and suggest you quick fixes.
Test your applicationsUpgrade Amazon-Linux:2023 perl-Net-DNS-tests to version 0:1.56-1.amzn2023.0.1 or higher.
This issue was patched in ALAS2023-2026-2046.
Note: Versions mentioned in the description apply only to the upstream perl-Net-DNS-tests package and not the perl-Net-DNS-tests package as distributed by Amazon-Linux.
See How to fix? for Amazon-Linux:2023 relevant fixed versions and status.
Net::DNS versions through 1.55 for Perl allow Denial of Service via deep DNS compression pointer chains.
Net::DNS::DomainName::decode follows RFC 1035 compression pointers by recursing into itself with no depth limit. It is possible to construct a name which saturates the call stack (at least with larger TCP responses), leading to a potential Denial of Service.
The guard $link < $offset prevents forward and circular chains, but still allows arbitrarily long backward chains. The per-offset cache ($cache) is populated at the start of each call and short-circuits only re-traverses of the same offset - the initial descent through a fresh chain still recurses at full depth.
A crafted packet can chain two-byte compression pointers so that each one points two bytes earlier than the previous, producing a chain length of offset / 2. For the 14-bit pointer field (max offset 16383) this gives up to 8191 recursive frames. For a TCP DNS message the limit is the 16-bit length field (32767 frames). Perl's default C stack handles only a few thousand frames; beyond that the process receives SIGSEGV or similar, which is a denial-of-service for any application parsing untrusted DNS data.
The vulnerability is triggered by Net::DNS::Packet->new(\$wire) i.e. any point where the library decodes a DNS message from the network.