Web Cache Poisoning

Summary

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.

Timeline

1. Feb 15, 2021, 12:15 PM UTCCVE published
2. Dec 17, 2025, 9:16 PM UTCCISA SSVC assessment

   Exploitation: none · Automatable: no · Technical impact: partial

3. Oct 14, 2026, 11:34 AM UTCRecord last updated
4. Oct 22, 2026EPSS reached 10%

   FIRST estimates at least a 10% chance of exploitation in the next 30 days

Affected versions

• 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

• djangoBitnami

  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

• libpythonBitnami

  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

• pythonBitnami

  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-minBitnami

  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

References 25