CVE & CISA-KEV Catalog

CVE-2021-23336

MEDIUMEPSS 98th pctl
5.9
CVSS v3
NVD

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.

CWE-444

CVSS v3 Vector

Exploitability

Attack VectorNetwork
Attack ComplexityHigh
Privileges RequiredNone
User InteractionRequired
ScopeUnchanged

Impact

ConfidentialityNone
IntegrityLow
AvailabilityHigh

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

Exploit Intelligence

37.33%probability of exploitation in 30 days
98thpercentile

Very high risk: more likely to be exploited than 98% of all known CVEs.

References

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This product uses NVD data but is not endorsed or certified by the NVD. EPSS scores courtesy of FIRST.org (https://www.first.org/epss). Source: CISA KEV Catalog. Data as of 2025-12-17.