CVE-2026-64194: CWE-674 Uncontrolled Recursion in NLNETLABS Net::DNS
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.
AI Analysis
Technical Summary
The Net::DNS Perl module (versions through 1.55) has a vulnerability (CWE-674) in its DNS compression pointer decoding function Net::DNS::DomainName::decode. The function recursively follows compression pointers as specified in RFC 1035 but lacks a limit on recursion depth. Although forward and circular pointer chains are prevented, arbitrarily long backward chains are allowed, enabling an attacker to create DNS messages that cause thousands of recursive calls. This leads to stack overflow and process termination (SIGSEGV), resulting in denial of service. The vulnerability is triggered when decoding DNS packets via Net::DNS::Packet->new. No patch or official fix has been published as of the data provided.
Potential Impact
An attacker can cause a denial of service by sending specially crafted DNS packets that exploit the uncontrolled recursion in the Net::DNS Perl module. This leads to stack exhaustion and crashes of any application using the vulnerable library to parse DNS messages, disrupting service availability. There is no impact on confidentiality or integrity reported.
Mitigation Recommendations
Patch status is not yet confirmed — check the vendor advisory for current remediation guidance. Until a fix is available, users should consider applying input validation or limiting the size and complexity of DNS messages processed by Net::DNS, or using alternative DNS parsing libraries that do not exhibit this vulnerability.
CVE-2026-64194: CWE-674 Uncontrolled Recursion in NLNETLABS Net::DNS
Description
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.
CVSS v3.1
Score 7.5high
Weaknesses
AI-Powered Analysis
Machine-generated threat intelligence
Technical Analysis
The Net::DNS Perl module (versions through 1.55) has a vulnerability (CWE-674) in its DNS compression pointer decoding function Net::DNS::DomainName::decode. The function recursively follows compression pointers as specified in RFC 1035 but lacks a limit on recursion depth. Although forward and circular pointer chains are prevented, arbitrarily long backward chains are allowed, enabling an attacker to create DNS messages that cause thousands of recursive calls. This leads to stack overflow and process termination (SIGSEGV), resulting in denial of service. The vulnerability is triggered when decoding DNS packets via Net::DNS::Packet->new. No patch or official fix has been published as of the data provided.
Potential Impact
An attacker can cause a denial of service by sending specially crafted DNS packets that exploit the uncontrolled recursion in the Net::DNS Perl module. This leads to stack exhaustion and crashes of any application using the vulnerable library to parse DNS messages, disrupting service availability. There is no impact on confidentiality or integrity reported.
Mitigation Recommendations
Patch status is not yet confirmed — check the vendor advisory for current remediation guidance. Until a fix is available, users should consider applying input validation or limiting the size and complexity of DNS messages processed by Net::DNS, or using alternative DNS parsing libraries that do not exhibit this vulnerability.
Technical Details
- Data Version
- 5.2
- Assigner Short Name
- CPANSec
- Date Reserved
- 2026-07-19T10:13:00.756Z
- Cvss Version
- null
- State
- PUBLISHED
- Remediation Level
- null
Threat ID: 6a5e6c132a4a8d5989888101
Added to database: 07/20/2026, 18:42:27 UTC
Last enriched: 07/30/2026, 12:37:50 UTC
Last updated: 09/03/2026, 22:52:13 UTC
Views: 85
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