CVE-2021-33026

9.8 CRITICAL 7% exploit odds Fix listed Code execution Server

What it is

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

At a glance

Exploitability: Can be exploited over the network without logging in. High risk of data exposure, data tampering, service disruption.
Exploit odds: 7.3% chance of exploitation in the next 30 days (EPSS).
Fix: A patch, advisory or fixed version is referenced. Upgrade or apply it.

Timeline

2021-05-13 00:00 UTC ReservedThe CVE id was reserved by its CNA
2021-05-13 23:15 UTC PublishedDisclosed publicly on CVE.org and NVD
2026-06-17 03:54 UTC Last updatedMost recent change to the record

Why it ranks here

Exploited in the wild: no, CISA does not list it.
Exploit odds: 7.3% in the next 30 days (EPSS).
Severity: 9.8 CRITICAL (CVSS).
Fix: a patch or advisory is linked.

Details

Published: 2021-05-13 23:15 UTC
Last modified: 2026-06-17 03:54 UTC
Exploit probability: 7.3% · EPSS, next 30 days
Weakness: CWE-502 · Unsafe deserialization
Record status: Modified

Affected

flask-caching Project flask-caching ≤ 1.10.1

Attack profile CVSS 3.1 · 9.8

Attack vector: Network
Complexity: Low
Privileges needed: None
User interaction: None
Scope: Unchanged
Confidentiality: High
Integrity: High
Availability: High

Raw vector

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

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-2021-33026.md and follow it. Check whether this project is affected by CVE-2021-33026. 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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Fix and advisories

References

NVD record · CVE.org record