CVE-2026-63311: medium-severity vulnerability in nltk
NLTK before 3.10.0 SSRF via DNS Resolution Failure
Published · Updated
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13Vexday Risk Score
No sign of exploitation. No public exploitation artifact known so far.
ssvc Trackcvss 6.9epss 0.3%
NLTK before 3.10.0 (affected versions <= 3.9.4) contains a server-side request forgery (SSRF) vulnerability in the validate_network_url() function in nltk/pathsec.py. The _resolve_hostname() helper catches OSError and ValueError during socket.getaddrinfo() and returns an empty list; when DNS resolution fails, the validation loop executes no IP checks and the function fails open, allowing urlopen() to proceed without validation. An attacker who can trigger DNS resolution failures or use DNS rebinding can bypass SSRF protections and reach restricted network resources, including cloud metadata endpoints (e.g., 169.254.169.254).
CVSS:4.0/AV:N/AC:L/AT:N/PR:N/UI:N/VC:N/VI:L/VA:N/SC:L/SI:L/SA:L
Affected products
nltk · nltkRelated CVEs — nltk
In the same product, most dangerous first.
CVE-2021-43854HIGHInefficient Regular Expression Complexity in nltkEPSS 2.8%CVE-2026-79657CRITICALNLTK before 3.10.3 Remote Code Execution via Unsafe Pickle DeserializationEPSS 1.3%CVE-2026-33231HIGHNLTK has unauthenticated remote shutdown in nltk.app.wordnet_appEPSS 1.2%CVE-2026-71513HIGHNLTK 3.10.0 through 3.10.2 Remote Code Execution via AllowlistUnpickler Dotted-Name BypassEPSS 1.1%CVE-2026-79675CRITICALNLTK before 3.10.3 JVM Argument Injection via Per-Call OptionsEPSS 0.8%CVE-2026-72818HIGHNLTK TweetTokenizer URL Pattern Backtracks Catastrophically on Naked-Domain-Like InputEPSS 0.7%