NLTK WekaClassifier flaw allows path traversal and sandbox bypass

CVE-2026-109956 (CVSS 7.0) in NLTK up to 3.10.3 lets attackers bypass the nltk.pathsec sandbox via caller-controlled model paths in WekaClassifier. The flaw enables arbitrary file overwrites and local file probing through the Weka JVM. It is fixed in NLTK 3.10.4.

• CVE-2026-109956: path traversal and sandbox bypass in WekaClassifier, CVSS 7.0
• Affects NLTK 3.10.3 and earlier; fixed in 3.10.4
• Weka JVM -d and -l arguments allow file overwrite and probing
• Exploit status is proof-of-concept; not listed in CISA KEV