CVE-2021-33026Network attack vector

Code execution via poisoned Pickle cache entry

Published May 13, 2021 · Updated Aug 3, 2024

Deserialization of untrusted data in Flask-Caching 1.10.1 and earlier allows attackers to execute Python code through a poisoned cache. The cache backends use Pickle to deserialize stored values, so loading a crafted entry invokes attacker-controlled Python object reconstruction. Exploitation requires arbitrary cache-write access, a colliding key, and an application read of the malicious entry; the maintainer considers that state already compromised.

CVSS severity4.2
Medium
EPSS probability7.01%
Next 30 days · Sep 16, 2026
Known exploitationUnconfirmed
Based on sourced intelligence
Hinoki checkNot available
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Summary

What happened

Deserialization of untrusted data in Flask-Caching 1.10.1 and earlier allows attackers to execute Python code through a poisoned cache. The cache backends use Pickle to deserialize stored values, so loading a crafted entry invokes attacker-controlled Python object reconstruction. Exploitation requires arbitrary cache-write access, a colliding key, and an application read of the malicious entry; the maintainer considers that state already compromised.

The record

CVE
CVE-2021-33026
Published
May 13, 2021
Updated
Aug 3, 2024
Vendor
Pallets Ecosystem
Product
Flask-Caching
Classifications
CWE-502, CWE-269, T1059.006
Attack vector
network
Privileges
admin

Timeline

How it unfolded

  1. May 13, 2021CVE publishedPublication date reported by the CVE source.
  2. Aug 3, 2024Record updatedLatest update available in the CVE record.

Exploitability

Present is not the same as exploitable

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Is a vulnerable build present?

Compare these published version ranges with your installed build and any vendor patches.

  1. Affected versionversion=0 <=1.10.1

What conditions does exploitation require?

Attack vectornetwork
Required privilegesadmin

What is affected?

Pallets Ecosystem · Flask-Cachingversion=0 <=1.10.1

Published CVSS scores

4.2GitHub Advisory DatabaseCVSS:3.1/AV:N/AC:H/PR:H/UI:R/S:U/C:N/I:H/A:N

CVSS describes severity. EPSS estimates exploitation probability.

Attacks

What attackers are doing with it

Daily unique IPs observed by Shadowserver honeypots for known exploited vulnerabilities (KEVs). Missing observations do not establish an absence of attacks.

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No observations available

Sep 10, 2026Sep 16, 2026
Latest reporting daySep 16, 2026
Latest daily unique IPsUnavailable
Prior 30-day averageUnavailable
SourceShadowserver honeypots (KEV)
Vectornetwork
Privilegesadmin
Known exploitationUnconfirmed
Public exploitUnconfirmed

Weakness, pattern, technique

CWE-502Deserialization of Untrusted Data
CWE-269Improper Privilege Management
T1059.006Command and Scripting Interpreter: Python

Public exploit references

No public exploit references are available in this record.

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Technologies

Your stack

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Your stack

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