EUVD-2026-71083Severity by source
AV:N/AC:L/PR:L/UI:N/S:U/C:L/I:N/A:N
AV:N (HTTP-triggered), AC:H (attacker must control PTR zone for their IP), PR:N (no target-app auth), A:L (thread-blocking DoS; no confidentiality or integrity impact).
Primary rating from Vendor (CPANSec).
CVSS VectorVendor: CPANSec
Lifecycle Timeline
4DescriptionCVE.org
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.
AnalysisAI
Unbounded synchronous DNS amplification in Robots::Validate for Perl (versions 0.3.2 through 0.3.10) allows a network attacker who controls the reverse DNS zone for their IP address to force arbitrarily many forward DNS lookups per validation call, exhausting server threads and causing application-level denial of service. The _check_dns FCRDNS loop issues one forward query per PTR record returned for the connecting IP, with no cap; Net::DNS's default TCP fallback for truncated UDP answers removes the 512-byte payload as a natural limit. …
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Attack ChainAIDerived
Hypothetical attack flow derived from CVE metadata
Vulnerability AssessmentAI
| Exploitation | Two simultaneous conditions must hold: (1) The attacker controls the reverse DNS zone for their connecting IP address and has crafted a PTR response with many hostnames matching the crawler domain configured in the target's Robots::Validate rules - this is achievable on cloud providers that allow PTR editing for allocated IPs. … Additional conditions and limiting factors are described in the full assessment. |
| Risk Assessment | The provided CVSS vector (CVSS:3.1/AV:N/AC:L/PR:L/UI:N/S:U/C:L/I:N/A:N, score 4.3) is inconsistent with the vulnerability class in two respects: the C:L (confidentiality low) impact is unrelated to the actual behavior, which is resource exhaustion, and A:N (no availability impact) contradicts the Denial of Service tag and the description. … Full risk analysis with EPSS, KEV, and SSVC signal comparison available after sign-in. |
| Exploit Scenario | Full exploit scenario with step-by-step reproduction available after sign-in. |
| Remediation | Upgrade Robots::Validate to v0.3.11 or later via CPAN (cpanm Robots::Validate). … Detailed patch versions, workarounds, and compensating controls in full report. |
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Same technique Denial Of Service
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External POC / Exploit Code
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