Medium [CVE-2026-80206] Denial of Service vulnerability in tgrep module
This medium-severity Red Hat Linux advisory covers CVE-2026-80206 affecting Exploit Intelligence, Lightspeed Core, OpenShift Lightspeed.
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Summary
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. A flaw was found in NLTK, specifically within its tgrep module.
This vulnerability, known as Regular Expression Denial of Service (ReDoS), allows a remote attacker to provide specially crafted regular expressions. When processed, these expressions can cause indefinite CPU saturation, leading to a complete denial of service for the Python process utilizing the NLTK library.
When processing user-supplied regular expressions inside /regex/ pattern nodes via functions such as tgrep_positions() or tgrep_compile(), NLTK executes re.search without input validation or execution timeouts.
If an application exposes these interfaces to unauthenticated or low-privileged attackers, supplying a specially crafted regular expression triggers catastrophic backtracking, resulting in CPU saturation and process-level denial of service.
- < 3.10.3
Official advisory · high-confidence parse· fetched 55 minutes ago·verify at source
Fixed versions
No fixed release is recorded yet. That does not prove no patch exists — confirm against the vendor advisory.
Official advisory · high-confidence parse· fetched 55 minutes ago·verify at source
Mitigation checklist
- Sanitize or restrict external input passed to NLTK's tgrep compilation functions to prevent execution of untrusted regular expressions, or enforce application-level timeouts using process isolation/multiprocessing wrappers to restrict CPU consumption.
Official advisory · high-confidence parse· fetched 55 minutes ago·verify at source
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