CVE-2026-81727

HIGHPre-NVD 7.17.1—
EchelonGraph scoreHIGH confidence

Score 7.1 from GitHub Security Advisory published 2026-08-27. a secondary CVSS source baseline 7.1; sources differ by 0.0.

Triggered by: GitHub Security Advisory CVSS
Sources: epss, ghsa, secondary
7.1EG
EchelonGraph verdictPlan a fixSerious severity, but no confirmed exploitation yet.
  • High severity, but no confirmed exploitation yet
CISA-KEV: Not listedEPSS PROB: 0%CVSS: 7.1Exploit: None knownExposed: 0

No vendor fix yet — apply a workaround or compensating control (WAF / firewall / segmentation) and watch for a patch.

NLTK versions before 3.10.3 contain a filesystem containment bypass vulnerability in the Downloader.download and Downloader.incr_download methods that allows attackers to overwrite files outside the install root through pre-existing hardlinks. Attackers with write access to a shared downloader directory can create hardlinks pointing to outside-root files that are then overwritten during normal package extraction, mutating files outside the intended install tree.

CVSS v3
7.1
EG Score
7.1(high)
EG Risk
37(Track)
EG Risk 37/100SSVC: Track

EG Risk is EchelonGraph's 0–100 priority score: it fuses intrinsic severity with real-world exploitation and automatability so you can rank equal-severity CVEs and fix the most dangerous first. Higher = act sooner. Distinct from the 0–10 EG Score (severity).

How it’s computed
Severity71% × 45%
Exploitation0% × 40%
Automatability30% × 15%
Action: Routine — remediate on your standard cadence.
EPSS PROB
0%
EPSS %ILE
3%
KEV
Not listed

Published

August 27, 2026

Last Modified

August 31, 2026

Advisory Details (2)

Auto-updated Aug 27, 2026
🔬 Proof of concept available. Patch available. Sources: github.
generic

NLTK before 3.10.3 Hardlink File Overwrite via downloader | Advisories | VulnCheck

https://www.vulncheck.com/advisories/nltk-before-3.10.3-hardlink-file-overwrite-via-downloader
github Patch Available🟡 PoC Available

Downloader.download follows hardlinks and overwrites outside-root files · Advisory · nltk/nltk · GitHub

https://github.com/nltk/nltk/security/advisories/GHSA-f794-5jv7-7672

Vendor Advisories for CVE-2026-81727(1)

These vendors published their own advisory mentioning this CVE — often with vendor-specific remediation steps + affected product lists not in NVD.

Affected Packages

(4 across 4 ecosystems)
Debian:12(1)
PackageVulnerable rangeFixed inDependents
nltk3.10.0-1 ... 3.9.3-1 (9 versions)——
Debian:13(1)
PackageVulnerable rangeFixed inDependents
nltk3.10.0-1 ... 3.9.3-1 (6 versions)——
Debian:14(1)
PackageVulnerable rangeFixed inDependents
nltk3.10.0-1, 3.10.1-1, 3.9.1-2, 3.9.2-1, 3.9.3-13.10.3-1—
PyPI(1)
PackageVulnerable rangeFixed inDependents
nltk0.8 ... 3.9b1 (68 versions)3.10.3—

Weakness Classification(1)

MITRE Common Weakness Enumeration — the root-cause categories this CVE belongs to.

Data Freshness Timeline

(refreshed 11× in last 7d / 53× in last 30d)

Each row is a source pipeline that fetched or updated this CVE on that date, with what changed. For example, "NVD update" means NVD published or revised its analysis for this CVE; "MITRE cvelistV5" means we ingested or refreshed it from the CNA feed. Most recent first.

  1. 2026-09-19 05:06 UTCEG score recompute
  2. 2026-09-18 19:28 UTCEPSS rescore
  3. 2026-09-17 01:22 UTCEG score recompute
  4. 2026-09-16 14:08 UTCEPSS rescore
  5. 2026-09-16 12:37 UTCEG score recompute
  6. 2026-09-16 05:15 UTCEPSS rescore
  7. 2026-09-15 11:07 UTCEG score recompute
  8. 2026-09-15 03:12 UTCEPSS rescore
  9. 2026-09-15 03:12 UTCEPSS rescore
  10. 2026-09-13 20:29 UTCEG score recompute
  11. 2026-09-12 18:59 UTCEG score recompute
  12. 2026-09-11 17:29 UTCEG score recompute
  13. 2026-09-11 14:53 UTCEPSS rescore
  14. 2026-09-11 14:53 UTCEPSS rescore
  15. 2026-09-10 15:35 UTCEG score recompute
  16. 2026-09-09 00:40 UTCEG score recompute
  17. 2026-09-08 22:01 UTCEPSS rescore
  18. 2026-09-07 17:14 UTCEG score recompute
  19. 2026-09-06 15:43 UTCEG score recompute
  20. 2026-09-06 13:48 UTCEPSS rescore
  21. 2026-09-05 01:26 UTCEG score recompute
  22. 2026-09-04 12:41 UTCEG score recompute
  23. 2026-09-04 05:07 UTCEPSS rescore
  24. 2026-09-02 22:17 UTCEG score recompute
  25. 2026-09-02 14:12 UTCEPSS rescore
Show 28 more
  1. 2026-09-02 09:32 UTCGHSA enrichment
  2. 2026-09-01 20:45 UTCEG score recompute
  3. 2026-09-01 20:45 UTCGHSA enrichment
  4. 2026-09-01 13:54 UTCEPSS rescore
  5. 2026-09-01 08:01 UTCEG score recompute
  6. 2026-09-01 08:01 UTCGHSA enrichment
  7. 2026-09-01 04:40 UTCEPSS rescore
  8. 2026-09-01 04:40 UTCEPSS rescore
  9. 2026-08-31 19:13 UTCGHSA enrichment
  10. 2026-08-31 10:57 UTCGHSA enrichment
  11. 2026-08-30 22:09 UTCEG score recompute
  12. 2026-08-30 22:09 UTCGHSA enrichment
  13. 2026-08-30 19:18 UTCEPSS rescore
  14. 2026-08-30 19:17 UTCEPSS rescore
  15. 2026-08-30 09:24 UTCEG score recompute
  16. 2026-08-30 09:24 UTCGHSA enrichment
  17. 2026-08-30 01:22 UTCEPSS rescore
  18. 2026-08-29 20:37 UTCGHSA enrichment
  19. 2026-08-29 07:50 UTCEG score recompute
  20. 2026-08-29 07:49 UTCGHSA enrichment
  21. 2026-08-28 21:42 UTCEPSS rescore
  22. 2026-08-28 19:03 UTCGHSA enrichment
  23. 2026-08-28 09:14 UTCGHSA enrichment
  24. 2026-08-27 20:27 UTCEG score recompute
  25. 2026-08-27 20:27 UTCGHSA enrichment
  26. 2026-08-27 17:24 UTCEG score recompute
  27. 2026-08-27 16:47 UTCEG score recompute
  28. 2026-08-27 16:43 UTCMITRE cvelistV5first tracked

Related CVEs(same CWE)

Frequently asked(5)

What is CVE-2026-81727?
CVE-2026-81727 is a high vulnerability published on August 27, 2026. NLTK versions before 3.10.3 contain a filesystem containment bypass vulnerability in the Downloader.download and Downloader.incr_download methods that allows attackers to overwrite files outside the install root through pre-existing hardlinks. Attackers with write access to a shared downloader…
When was CVE-2026-81727 disclosed?
CVE-2026-81727 was first published in the National Vulnerability Database on August 27, 2026, with the most recent update on August 31, 2026. EchelonGraph re-ingests CVE updates from NVD on a 2-hour cycle, so this page reflects the latest published state.
Is CVE-2026-81727 actively exploited?
CVE-2026-81727 is not currently on CISA's Known Exploited Vulnerabilities catalog. FIRST EPSS estimates a 0% probability of exploitation in the next 30 days, which ranks it in the top 96.6% of all scored CVEs.
What is the CVSS score of CVE-2026-81727?
CVE-2026-81727 has a CVSS v3 base score of 7.1 (NVD).
How do I remediate CVE-2026-81727?
Patch to the fixed version published by the affected vendor. Where vendor advisories exist for CVE-2026-81727, EchelonGraph cross-links them in the Vendor Advisories panel below — those typically contain the canonical remediation steps, fixed version numbers, and any vendor-specific mitigations.

Dependency Blast Radius

See which npm, PyPI, Go, and Maven packages are affected by CVE-2026-81727

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