CVE-2026-81727: NLTK versions before 3.10.3 contain a filesystem containment bypass vulnerability in the Downloader.download a

Q: How do I fix CVE-2026-81727?

nltk: upgrade to 3.10.3. Exact commands for each OS are on this page.

Q: Is CVE-2026-81727 being exploited?

CVE-2026-81727 is not on the CISA Known Exploited Vulnerabilities list at the time of the last update. Check again, as this can change.

Q: What does CVE-2026-81727 affect?

CVE-2026-81727 affects nltk. Severity is high (CVSS 7.1). 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 hardlin

Q: How urgent is CVE-2026-81727?

Priority 32/100. High severity; Public exploit reference

Routine

HIGH 7.1UPGRADE

CVE-2026-81727 is a high-severity flaw (CVSS 7.1) affecting nltk. Below: why it ranks where it does, which versions are affected, what to do, and the exact commands.

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 intend

Why this priority

High severity
Public exploit reference

A fixed release or distro patch exists.

Risk facts

CVSS score	7.1 (High)
Attack vector	Local
Attack complexity	Low
Privileges needed	Low
User interaction	None
EPSS exploit chance	0.2% (top 92%)
CISA exploited list	No
Weakness	CWE-59
Published	2026-08-27
Last modified	2026-08-31

Publisher (CNA): VulnCheck · Vendor: nltk

Last updated 2026-08-31 · Sources: CVE Program, NVD, CISA KEV, EPSS and vendor advisories · How we score

Am I affected?

Timeline

2026-08-27 17:21 UTCPublished CVE record published
2026-08-31 19:08 UTCUpdated Record last modified

nltk nltk UPGRADE

Affected: < 3.10.3

Fixed in: 3.10.3

Safe to downgrade to: no unaffected older release

1. Check installed version

apt-cache policy nltk || rpm -q nltk || nltk --version

2. UPGRADE to 3.10.3 (Debian / Ubuntu)

sudo apt update && sudo apt install --only-upgrade nltk

2. UPGRADE (RHEL / Amazon Linux / Fedora)

sudo dnf upgrade nltk

Note

Distros often backport fixes without changing the version number. Confirm with the distro advisory or changelog.

Verify at the official source NVD · CVE Program · Report a problem with this page
Scores and fixes here are computed automatically from those and other public sources. Confirm with the vendor advisory before changing production systems.

Quick answers

How do I fix CVE-2026-81727?

nltk: upgrade to 3.10.3. Exact commands for each OS are on this page.

Is CVE-2026-81727 being exploited?

CVE-2026-81727 is not on the CISA Known Exploited Vulnerabilities list at the time of the last update. Check again, as this can change.

What does CVE-2026-81727 affect?

CVE-2026-81727 affects nltk. Severity is high (CVSS 7.1). 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 hardlin

How urgent is CVE-2026-81727?

Priority 32/100. High severity; Public exploit reference

Related CVEs

CVE-2026-12252 HIGH 7.8 UPGRADE In nltk/nltk versions 3.9.3 and earlier, five Stanford interface classes (StanfordPOSTagger, StanfordNERTagger
CVE-2026-12259 MEDIUM 6.5 DOWNGRADE In nltk version 3.9.4, the `nltk.downloader.Downloader._download_package()` function writes downloaded package
CVE-2026-12261 MEDIUM 6.5 UPGRADE A vulnerability in `nltk.downloader` in nltk/nltk versions <= 3.9.4 allows for cross-package resource and mode
CVE-2026-12372 LOW 3.7 DOWNGRADE A Server-Side Request Forgery (SSRF) vulnerability exists in nltk/nltk versions 3.9.4 and the current develop
CVE-2026-71513 HIGH 8.8 UPGRADE NLTK before 3.10.3 contains a remote code execution vulnerability in AllowlistUnpickler that validates only th

References

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