CVE-2026-79657 NLTK before 3.10.3 Remote Code Execution via Unsafe Pickle Deserialization
Attackers can execute arbitrary code by crafting malicious pickle payloads that exploit unsafe deserialization in NLTK's allowlisted loaders.
- Exploited in the wild
- Not known
- Login needed
- Not needed
- Attackable
- Over the internet
- Victim action needed
- Not needed
- Fix
- Available
What is CVE-2026-79657?
CVE-2026-79657 is a critical unsafe deserialization vulnerability in nltk, published on 25 Aug 2026. An attacker can exploit it over the internet without logging in, with no action from the victim.
Official description
NLTK versions before 3.10.3 contain a remote code execution vulnerability in allowlisted pickle loaders that trust entire module namespaces instead of specific safe callables. Attackers can craft malicious pickle payloads invoking dangerous in-namespace functions like ReppTokenizer._execute and numpy.f2py.crackfortran.myeval through pickle REDUCE to execute arbitrary commands during model or tokenizer artifact loading.
Weakness: CWE-502
Which versions are affected by CVE-2026-79657?
3 open source packages ship an affected version, including nltk. It affects 1 product.
| Package | Affected | Fixed in |
|---|---|---|
nltk PyPI | All versions | 3.10.3 |
nltk PyPI | All versions | 3.10.3 |
nltk PyPI | All versions | 3.10.3 |
Products include Nltk Nltk.
How do I fix CVE-2026-79657?
Upgrade nltk to 3.10.3 or later.
Upgrade, and only deserialise data from trusted sources or with an allow-list of types. More about Unsafe deserialization.
Is CVE-2026-79657 being exploited?
It is not confirmed as exploited in the wild, but public exploit code for CVE-2026-79657 exists.
Other vulnerabilities in nltk
- CVE-2026-0848 Arbitrary Code Execution in NLTK StanfordSegmenter via Untrusted JAR Loading
- CVE-2025-14009 Zip Slip Vulnerability in nltk/nltk Leading to Remote Code Execution
- CVE-2026-78683 NLTK before 3.10.0 Remote Code Execution via Unsafe Pickle Deserialization
- CVE-2026-79675 NLTK before 3.10.3 JVM Argument Injection via Per-Call Options
- CVE-2026-79674 NLTK 3.10.2 Path Traversal via corpus-reader constructors
Sources
Also known as DEBIAN-CVE-2026-79657, ECHO-68fb-b254-885c, GHSA-x99w-6fgc-pmfw, MINI-5j8f-vxr3-xc66, PYSEC-2026-3735, UBUNTU-CVE-2026-79657.