CVE-2026-63311Public exploitNetwork attack vector

SSRF via fail-open DNS resolution

Published Aug 22, 2026 · Updated Aug 22, 2026

SSRF in NLTK before 3.10.0 allows remote attackers to reach restricted network resources when hostname resolution fails. In nltk/pathsec.py, _resolve_hostname() converts socket.getaddrinfo() errors into an empty list, so validate_network_url() performs no address checks and urlopen() proceeds. Reachability requires an application to pass attacker-controlled URLs into NLTK and a transient or attacker-induced DNS failure; successful requests can access internal services or cloud metadata.

CVSS severity6.9
Medium
EPSS probability0.24%
Next 30 days · Sep 16, 2026
Known exploitationUnconfirmed
Based on sourced intelligence
Hinoki checkNot available
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Summary

What happened

SSRF in NLTK before 3.10.0 allows remote attackers to reach restricted network resources when hostname resolution fails. In nltk/pathsec.py, _resolve_hostname() converts socket.getaddrinfo() errors into an empty list, so validate_network_url() performs no address checks and urlopen() proceeds. Reachability requires an application to pass attacker-controlled URLs into NLTK and a transient or attacker-induced DNS failure; successful requests can access internal services or cloud metadata.

The record

CVE
CVE-2026-63311
Published
Aug 22, 2026
Updated
Aug 22, 2026
Vendor
NLTK Project
Product
NLTK
Classifications
CWE-918
Attack vector
network
Privileges
unauthenticated

Timeline

How it unfolded

  1. Aug 22, 2026CVE publishedPublication date reported by the CVE source.
  2. Aug 22, 2026Record updatedLatest update available in the CVE record.

Exploitability

Present is not the same as exploitable

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Is a vulnerable build present?

Compare these published version ranges with your installed build and any vendor patches.

  1. Affected versionversion=0 <3.10.0

What conditions does exploitation require?

Attack vectornetwork
Required privilegesunauthenticated

What is affected?

NLTK Project · NLTKversion=0 <3.10.0

Published CVSS scores

6.9UbuntuCVSS:4.0/AV:N/AC:L/AT:N/PR:N/UI:N/VC:N/VI:L/VA:N/SC:L/SI:L/SA:L
5.3UbuntuCVSS:3.1/AV:N/AC:L/PR:N/UI:N/S:U/C:N/I:L/A:N

CVSS describes severity. EPSS estimates exploitation probability.

Attacks

What attackers are doing with it

Daily unique IPs observed by Shadowserver honeypots for known exploited vulnerabilities (KEVs). Missing observations do not establish an absence of attacks.

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No observations available

Sep 10, 2026Sep 16, 2026
Latest reporting daySep 16, 2026
Latest daily unique IPsUnavailable
Prior 30-day averageUnavailable
SourceShadowserver honeypots (KEV)
Vectornetwork
Privilegesunauthenticated
Known exploitationUnconfirmed
Public exploitPublished

Weakness, pattern, technique

CWE-918Server-Side Request Forgery (SSRF)

Public exploit references

Labels summarize the accepted research assessment. They do not indicate a test against your environment.

Technologies

Your stack

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Your stack

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