nltk PorterStemmer in versions <= 3.10.2 (fixed in 3.10.3) contains an inefficient-algorithmic-complexity denial of service in PorterStemmer.stem(). The _is_consonant() helper walks backward over the entire run of trailing y characters on every call, and _measure() invokes it for each stem position, causing O(n^2) behavior. A single ~20-50 KB untrusted token consisting of a long run of the letter y followed by a matching suffix (e.g., ness) can pin a CPU core for seconds to minutes, causing availability impact.
Weakness
An algorithm in a product has an inefficient worst-case computational complexity that may be detrimental to system performance and can be triggered by an attacker, typically using crafted manipulations that ensure that the worst case is being reached.
Affected Software
| Name | Vendor | Start Version | End Version |
|---|---|---|---|
| Nltk | Nltk | * | 3.10.3 (excluding) |
| Red Hat OpenShift AI 3.5 | RedHat | rhoai/odh-ta-lmes-job-rhel9:1788935863 | * |
| Nltk | Ubuntu | upstream | * |