CVE-2026-78682 — NLTK before 3.10.3 SSRF Protection Bypass via Proxy
NLTK before 3.10.3 contains a server-side request forgery vulnerability in nltk.pathsec.urlopen (and callers nltk.data.load, nltk.downloader.Downloader.index/download) when an HTTP proxy is configured. pathsec.urlopen validates the requested hostname locally, but proxy-handler inheritance disables the safe HTTP/HTTPS handlers so the actual fetch is performed by the proxy against a destination that is never re-validated. An attacker can supply a validated public URL that the proxy forwards to an internal loopback-only service, allowing disclosure of internal HTTP resources, loading of forged downloader indexes, and installation of attacker-chosen package content.
Who exploits it and how urgent it is
A 0–100 score combining confirmed exploitation, ransomware and APT use, public exploits, EPSS and severity.
How the score was calculated
- EPSS 0.4% (30-day exploitation probability)+5
- Technical severity (high)+6
- CISA SSVC: exploitation "poc"+5
- Automatable exploitation (SSVC)+3
The score orders the patch queue; it does not replace your asset context (internet exposure, criticality, compensating controls).
Triage
Is it exploited, how likely is exploitation, what does it touch, and how severe do the sources call it.
CISA SSVC assessment CISA
Three decision points CISA publishes for the CVEs it assesses (SSVC 2.0.3). A stakeholder decision, not a severity score.
Remediation
Fixes and mitigations documented by the sources — linked to the original advisory.
- Pip Nltk: fixed in version 3.10.3 — github.com (GitHub Security Advisories)
First 24 hours
Ordered from the record’s own fields — exposure first, because you cannot patch what you have not found. A rule-generated starting point.
- Identify exposed assets running the affected vendor/product/version combinations (Nltk Nltk, Pip Nltk).
- The attack is network-based and needs no privileges: restrict exposure (ACLs, VPN, WAF) until patched.
- Apply the fixed version or the patch documented under Remediation.
- Search available logs for exploit probes matching the vulnerability class (ssrf), errors and authentication anomalies.
Affected scope
Vendor, product and versions as the sources word them.
Attack characteristics
The CVSS vector, decoded. It describes the attack, not your exposure to it.
Every base score collected
Sources score independently and may disagree; each row says who scored it and under which version.
| Score | Version | Severity | Expl. | Impact | Scored by |
|---|---|---|---|---|---|
| 8.7 | CVSS 4.0 | High | — | — | disclosure@vulncheck.com via NIST National Vulnerability Database |
| 8.7 | CVSS 4.0 | High | — | — | VulnCheck via CVE Program (cve.org) e CISA ADP |
| 7.5 | CVSS 3.1 | High | 3.9 | 3.6 | disclosure@vulncheck.com via NIST National Vulnerability Database |
| 7.5 | CVSS 3.1 | High | — | — | VulnCheck via CVE Program (cve.org) e CISA ADP |
CVSS:3.1/AV:N/AC:L/PR:N/UI:N/S:U/C:H/I:N/A:N (score shown at the top: disclosure@vulncheck.com) Weakness MITRE
Weakness class according to MITRE’s CWE catalog.
EPSS over time FIRST
Oct 13, 2026 → Oct 14, 2026 · 2 reading(s) · max 0.44%
Detection
Read off the CVSS vector and the weakness class. Starting points, not tested rules.
- Prioritize edge telemetry for the network-reachable component (proxy, WAF, IDS/IPS).
- Monitor outbound requests from the server to internal IPs and cloud metadata endpoints.
Timeline
What happened to this CVE, newest first.
- 2026
- Fix documented
- Affected products added · pip/nltk
- Affected products added · nltk/nltk
- SSVC assessment updated
- Record published
- CVSS changed · 7.5
- Source status changed · → Analyzed
- Record created in this database
- CVE published
Source activity
Repeated readings are counted rather than listed.
- 1× References added · Oct 13, 2026 – Oct 13, 2026
- 1× Official description updated · Oct 13, 2026 – Oct 13, 2026
References
7 on the record
- github.com/nltk/nltk/security/advisories/GHSA-6ww7-3frv-cqxh
- www.vulncheck.com/advisories/nltk-before-ssrf-protection-bypass-via-proxy
- github.com/advisories/GHSA-6ww7-3frv-cqxh
- github.com/nltk/nltk/releases/tag/v3.10.3
- github.com/pypa/advisory-database/tree/main/vulns/nltk/PYSEC-2026-3733.yaml
- nvd.nist.gov/vuln/detail/CVE-2026-78682
- github.com/nltk/nltk/commit/767333a005a1cd3d82d2029215f2dbe66a5844d9
Elsewhere on this site
Related CVEs (same products)
- High CVE-2026-109956 NLTK through 3.10.3 Path Traversal via WekaClassifier Model Path 2d
- High CVE-2026-81727 Link Following in Nltk Aug 27, 2026
- Medium CVE-2026-81724 Uncontrolled Recursion in Nltk Aug 27, 2026
- Low CVE-2026-81725 Uncontrolled Resource Consumption in Nltk Aug 27, 2026
- High CVE-2026-81726 NLTK through 3.10.3 contains a path traversal vulnerability in model-artifact APIs that… Aug 27, 2026
- High CVE-2026-81722 nltk PorterStemmer in versions Aug 27, 2026
Not in any source we poll
Listed rather than left blank: an empty field and an unmeasured one look identical on screen, and only one is a reason to look elsewhere.
- No confirmed IOCs, IP addresses, domains, file hashes, or malware artifacts supplied.
- No organization-specific asset inventory, compensating-control status, or patch deployment evidence supplied.
- No exploit packet captures, log samples, or incident case IDs supplied.
Answered from this record
Text assembled only from the fields above — no additional claims.
What should defenders know first?
CVE-2026-78682 is "NLTK before 3.10.3 SSRF Protection Bypass via Proxy", rated High. It affects Nltk (Nltk); versions are in the scope table. It is not in CISA KEV, which does not rule out exploitation. CVSS 7.5 describes technical severity. EPSS 0.44% estimates the probability of exploitation in 30 days; neither replaces your asset context. First verify whether exposed or business-critical assets run the affected versions, apply vendor fixes or mitigations, and preserve logs for review.
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