EUVD-2026-64334
GHSA-qg9p-xrhj-435m
Severity by source
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/E:X/CR:X/IR:X/AR:X/MAV:X/MAC:X/MAT:X/MPR:X/MUI:X/MVC:X/MVI:X/MVA:X/MSC:X/MSI:X/MSA:X/S:X/AU:X/R:X/V:X/RE:X/U:X
AC:H for DNS rebinding or engineered resolution failure prerequisite; S:C and C:L/I:L reflect cross-boundary access to cloud metadata and internal services.
Primary rating from Vendor (VulnCheck).
CVSS VectorVendor: VulnCheck
Lifecycle Timeline
2Blast Radius
ecosystem impact- 7 pypi packages depend on nltk (6 direct, 1 indirect)
Ecosystem-wide dependent count for version 3.10.0.
DescriptionCVE.org
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).
AnalysisAI
SSRF protection bypass in NLTK affects all versions before 3.10.0, where a fail-open logic error in validate_network_url() allows attackers to reach restricted network resources including cloud metadata endpoints such as 169.254.169.254. The flaw resides in _resolve_hostname(), which silently swallows OSError and ValueError from socket.getaddrinfo() and returns an empty list; the subsequent IP validation loop then iterates zero times, allowing urlopen() to execute the request with no filtering applied. …
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Attack ChainAIDerived
Hypothetical attack flow derived from CVE metadata
Vulnerability AssessmentAI
| Exploitation | Exploitation requires all three of the following: (1) the target application must invoke NLTK's validate_network_url() function or a higher-level NLTK function that calls it, with a URL value that the attacker can influence - NLTK itself is a library and does not expose a network service, so the application's exposure surface determines whether this condition is met; (2) the attacker must be able to engineer a DNS resolution failure for the supplied hostname (e.g., by supplying a domain returning NXDOMAIN, or controlling DNS to produce an OSError or ValueError from socket.getaddrinfo()) or execute a DNS rebinding attack where a domain resolves to a permitted public IP during validation but to a restricted internal IP at request time; (3) for the highest-impact scenario, the deployment environment must have a reachable link-local metadata endpoint (169.254.169.254) without IMDSv2 or equivalent enforcement. … Additional conditions and limiting factors are described in the full assessment. |
| Risk Assessment | The vendor-supplied CVSS 4.0 vector (AV:N/AC:L/AT:N/PR:N/UI:N/VC:N/VI:L/VA:N/SC:L/SI:L/SA:L) yields a score of 6.9, characterizing this as a remotely exploitable, low-complexity flaw with no authentication requirement and collateral impact on subsequent systems. … 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 NLTK to version 3.10.0, which contains the vendor-released patch correcting the fail-open behavior in _resolve_hostname(). … Detailed patch versions, workarounds, and compensating controls in full report. |
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Same weakness CWE-918 – Server-Side Request Forgery (SSRF)
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External POC / Exploit Code
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