CVE-2026-82309
Received Received - Intake

DNS Exhaustion Flaw in Robots::Validate Perl Module

Publication date: 2026-09-04

Last updated on: 2026-09-04

Assigner: CPANSec

Description
Robots::Validate versions from 0.3.2 before 0.3.11 for Perl allow unbounded outbound DNS queries per validation via a forward-confirmation loop that does not bound the names it queries. _check_dns issues one PTR query for the client address, keeps the returned names matching the rule's domain, and issues a forward query for each until one resolves back to that address. Nothing bounds that list, and a client controls the reverse zone for its own address, so it chooses how many names the PTR answer holds. Net::DNS refetches a truncated answer over TCP by default, so the 512-byte UDP payload does not cap it either. Any client whose User-Agent matches a rule with a domain reaches _check_dns. Each forward name is distinct and client-chosen, so every query misses the local cache and is resolved against the authoritative servers for that domain. The queries are synchronous, so the caller is held until all of them answer or time out.

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Meta Information

Published
2026-09-04
Last Modified
2026-09-04
Generated
2026-09-04
AI Q&A
2026-09-04
EPSS Evaluated
N/A
NVD
CVE-2026-82309
EUVD
EUVD-2026-71083

Affected Vendors & Products

Showing 1 associated CPE
Vendor Product Version / Range
robrwo robots_validate to 0.3.11 (exc)

Helpful Resources

Exploitability

CWE
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KEV
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CWE ID Description
CWE-405 The product does not properly control situations in which an adversary can cause the product to consume or produce excessive resources without requiring the adversary to invest equivalent work or otherwise prove authorization, i.e., the adversary's influence is "asymmetric."
CWE-770 The product allocates a reusable resource or group of resources on behalf of an actor without imposing any intended restrictions on the size or number of resources that can be allocated.

Attack-Flow Graph

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Executive Summary

This vulnerability in Robots::Validate for Perl allows attackers to trigger an unbounded number of outbound DNS queries per HTTP request. The issue occurs in the _check_dns function, which performs forward DNS confirmation for every PTR record matching a rule's domain without any limit. Since clients control their reverse DNS zone, they can manipulate the number of PTR records returned, causing excessive synchronous DNS lookups that block the worker thread.

Detection Guidance

Monitor for excessive DNS queries originating from systems running Robots::Validate versions 0.3.2 to 0.3.10. Check for repeated PTR and forward DNS lookups from the same client IP, especially if they match User-Agent rules. Use tools like tcpdump or Wireshark to capture DNS traffic and identify patterns of unbounded queries.

Impact Analysis

This vulnerability can lead to denial-of-service attacks by exhausting system resources. Each malicious request can trigger many DNS queries, consuming network bandwidth, CPU, and memory. It may also slow down or crash the application due to synchronous blocking calls that wait up to 30 seconds for unresponsive DNS servers. Systems using greedy mode are especially vulnerable as it multiplies queries by checking every substring in the User-Agent.

Compliance Impact

This vulnerability could lead to resource exhaustion attacks that may disrupt services handling sensitive data, potentially violating GDPR's availability principle or HIPAA's security requirements for reliable access to protected health information.

Mitigation Strategies

Upgrade Robots::Validate to version 0.3.11 or later, which includes a default limit of 4 forward lookups per rule. Disable the greedy mode if enabled, as it exacerbates the issue by multiplying queries. Monitor DNS query volumes and block suspicious IPs generating excessive lookups.

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