CVE-2026-121577

What it is

Inefficient Regular Expression Complexity (CWE-1333) in generate_regex() (whatstk/whatsapp/parser.py) in whatstk from 0.2.0 before 0.9.0 allows a party that supplies a chat export to consume the CPU of the process that parses it for an unbounded time, because the function builds the header regular expression by replacing each %x code with its named capture group and leaves every other character of the header format in the pattern unescaped. A header whose date separator is a regular expression metacharacter therefore alters the pattern instead of matching itself: a separator of + quantifies the preceding capture group, giving (?P<day>\d{1,2})+(?P<month>\d{1,2})+(?P<year>\d{2,4}), and a run of digits that cannot complete the header then makes the engine try every way of partitioning that run. Header auto detection is enabled by default and derives the format from the text of the file, so the separator is taken from the export itself and no header format has to be passed by the caller. Separators of (, ) and \ instead raise re.PatternError, separators of *, | and ? raise TypeError, and separators of ^ and $ raise KeyError, none of which the library catches. This results in the parse of a file of a few hundred bytes consuming CPU without completing, or in an uncaught exception in the calling program.

At a glance

Exploitability

Can be exploited locally on the machine without logging in, but needs a user to act. High risk of service disruption.

Exploit odds

0.1% chance of exploitation in the next 30 days (EPSS).

Fix

A patch, advisory or fixed version is referenced. Upgrade or apply it.

Timeline

1. 2026-11-03 15:29 UTC ReservedThe CVE id was reserved by its CNA
2. 2026-11-03 20:18 UTC PublishedDisclosed publicly on CVE.org and NVD
3. 2026-11-06 20:17 UTC Last updatedMost recent change to the record

Why it ranks here

• Exploited in the wild: no, CISA does not list it.
• Exploit odds: 0.1% in the next 30 days (EPSS).
• Severity: 6.7 MEDIUM (CVSS).
• Fix: a patch or advisory is linked.

Details

Published

2026-11-03 20:18 UTC

Last modified

2026-11-06 20:17 UTC

Exploit probability

0.1% · EPSS, next 30 days

Weakness

CWE-1333

Record status

Received

Attack profile CVSS 4.0 · 6.7

Attack vector

Local

Complexity

Low

Attack requirements

None

Privileges needed

None

User interaction

Active

Confidentiality

None

Integrity

None

Availability

High

Is it in your code?

Hand this to your coding agent. It searches your project for the affected products and checks versions. Nothing leaves your machine.

Read https://cve-list.com/agent/cve/CVE-2026-121577.md and follow it. Check whether this project is affected by CVE-2026-121577. Read only. Don't change anything and don't upload my code. Tell me yes, no or not sure, with the file as proof.

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