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Vulnerability record · CVE-2021-33026 · published 13 May 2021

CVE-2021-33026: Flask-caching project flask-caching deserialization of untrusted data vulnerability

FFlask Caching Project · Flask Caching

The Flask-Caching extension through 1.10.1 for Flask relies on Pickle for serialization, which may lead to remote code execution or local privilege escalation. If an attacker gains access to cache storage (e.g., filesystem, Memcached, Redis, etc.), they can construct a crafted payload, poison the cache, and execute Python code. NOTE: a third party indicates that exploitation is extremely unlikely unless the machine is already compromised; in other cases, the attacker would be unable to write their payload to the cache and generate the required collision

9.8 CVSS 3.1 Critical EPSS 7.1% · top 6.0% CWE-502 · Deserialization of untrusted data
9.8CVSS 3.1 base score, v2 7.5
7.1%EPSS exploitation probability, 30 days
NoNot in CISA KEV
1Affected product versions listed by NVD
4References
17 Jun 2026Last modified by NVD

Description

The Flask-Caching extension through 1.10.1 for Flask relies on Pickle for serialization, which may lead to remote code execution or local privilege escalation. If an attacker gains access to cache storage (e.g., filesystem, Memcached, Redis, etc.), they can construct a crafted payload, poison the cache, and execute Python code. NOTE: a third party indicates that exploitation is extremely unlikely unless the machine is already compromised; in other cases, the attacker would be unable to write their payload to the cache and generate the required collision

CVSS:3.1/AV:N/AC:L/PR:N/UI:N/S:U/C:H/I:H/A:H

Affected products

1 vulnerable configurations from NVD's CPE data, grouped by vendor and product.

References

LinkTags
https://github.com/pallets-eco/flask-caching/pull/209#issuecomment-1136397937 Issue TrackingPatchThird Party Advisory
https://github.com/sh4nks/flask-caching/pull/209 PatchThird Party Advisory
https://github.com/pallets-eco/flask-caching/pull/209#issuecomment-1136397937 Issue TrackingPatchThird Party Advisory
https://github.com/sh4nks/flask-caching/pull/209 PatchThird Party Advisory

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Source: NIST National Vulnerability Database (record CVE-2021-33026), CISA KEV, FIRST EPSS (scores of 2026-09-26). This page is refreshed as NVD updates the record.