CVE-2026-80206: NLTK before 3.10.3 contains a regular expression denial of service (ReDoS) vulnerability in the tgrep module

Q: How do I fix CVE-2026-80206?

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

Q: Is CVE-2026-80206 being exploited?

CVE-2026-80206 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-2026-80206 affect?

CVE-2026-80206 affects nltk. Severity is medium (CVSS 5.9). NLTK before 3.10.3 contains a regular expression denial of service (ReDoS) vulnerability in the tgrep module. The _tgrep_node_action function compiles user-supplied regular expressions embedded in /regex/ pattern nodes and executes them via

Q: How urgent is CVE-2026-80206?

Priority 40/100. Public exploit reference; Remotely exploitable, no login, no user action

This week

MEDIUM 5.9REMOTEUPGRADE

CVE-2026-80206 is a medium-severity flaw (CVSS 5.9) affecting nltk. Below: why it ranks where it does, which versions are affected, what to do, and the exact commands.

NLTK before 3.10.3 contains a regular expression denial of service (ReDoS) vulnerability in the tgrep module. The _tgrep_node_action function compiles user-supplied regular expressions embedded in /regex/ pattern nodes and executes them via re.search against tree node labels without any validation or timeout. An attacker who controls the tgrep pattern (e.g., via tgrep_positions() or tgrep_compile() exposed to external input) can supply a pattern

Why this priority

Public exploit reference
Remotely exploitable, no login, no user action

A fixed release or distro patch exists.

Risk facts

CVSS score	5.9 (Medium)
Attack vector	Network (remote)
Attack complexity	High
Privileges needed	None
User interaction	None
EPSS exploit chance	0.4% (top 62%)
CISA exploited list	No
Weakness	CWE-1333
Published	2026-08-26
Last modified	2026-09-01

Publisher (CNA): VulnCheck · Vendor: nltk

Last updated 2026-09-01 · Sources: CVE Program, NVD, CISA KEV, EPSS and vendor advisories · How we score

Am I affected?

Timeline

2026-08-26 11:16 UTCPublished CVE record published
2026-09-01 20:07 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-2026-80206?

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

Is CVE-2026-80206 being exploited?

CVE-2026-80206 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-2026-80206 affect?

CVE-2026-80206 affects nltk. Severity is medium (CVSS 5.9). NLTK before 3.10.3 contains a regular expression denial of service (ReDoS) vulnerability in the tgrep module. The _tgrep_node_action function compiles user-supplied regular expressions embedded in /regex/ pattern nodes and executes them via

How urgent is CVE-2026-80206?

Priority 40/100. Public exploit reference; Remotely exploitable, no login, no user action

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References

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