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CVE-2026-80206

HighCVSS 8.2 / 10
Published Aug 26, 2026·Last modified Aug 27, 2026
Affected Components(49)
nltk/nltk
3.6.2
nltk/nltk
3.6.5
nltk/nltk
3.10.0
1 / 17
Description

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 that triggers catastrophic backtracking, causing indefinite CPU saturation that blocks the Python process.

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Risk Scores
Base Score
8.2

The vulnerability can be exploited over the network without needing physical access. It is difficult for an attacker to exploit this vulnerability and may require special conditions. An attacker does not need any special privileges or access rights. No user interaction is needed for the attacker to exploit this vulnerability.

Threat Intelligence
4.6

Exploitation attempts have been detected. Elevated vigilance and prompt remediation are advised.

EPSS
0.44%

The exploit probability is very low. The vulnerability is unlikely to be exploited in the next 30 days.

Exploit
Not available

We did not find any exploit available. Neither in GitHub repositories nor in the Exploit-Database.

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