CVE-2021-20211Network attack vector

Service crash via client-tag memory leak

Published Mar 25, 2021 · Updated Aug 3, 2024

Memory leakage in Privoxy before 3.0.29 allows remote attackers to crash the proxy service through requests while client tags are active. Privoxy fails to release memory while processing requests under active client-tag rules, so repeated traffic progressively consumes available memory. Exploitation requires configured client tags and affects availability only, ultimately crashing the process or its host.

CVSS severity7.5
High
EPSS probability2.15%
Next 30 days · Sep 16, 2026
Known exploitationUnconfirmed
Based on sourced intelligence
Hinoki checkNot available
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Summary

What happened

Memory leakage in Privoxy before 3.0.29 allows remote attackers to crash the proxy service through requests while client tags are active. Privoxy fails to release memory while processing requests under active client-tag rules, so repeated traffic progressively consumes available memory. Exploitation requires configured client tags and affects availability only, ultimately crashing the process or its host.

The record

CVE
CVE-2021-20211
Published
Mar 25, 2021
Updated
Aug 3, 2024
Vendor
Privoxy Developers
Product
Privoxy
Classifications
CWE-401, T1499.004
Attack vector
network
Privileges
unauthenticated

Timeline

How it unfolded

  1. Mar 25, 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=Privoxy 3.0.29

What conditions does exploitation require?

Attack vectornetwork
Required privilegesunauthenticated

What is affected?

Privoxy Developers · Privoxyversion=Privoxy 3.0.29

Published CVSS scores

7.8NIST NVDAV:N/AC:L/Au:N/C:N/I:N/A:C
7.5NIST NVDCVSS:3.1/AV:N/AC:L/PR:N/UI:N/S:U/C:N/I:N/A:H

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.

Daily unique IPsNo honeypot observations are available for this CVE in the selected window.

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
Privilegesunauthenticated
Known exploitationUnconfirmed
Public exploitUnconfirmed

Weakness, pattern, technique

CWE-401Missing Release of Memory after Effective Lifetime
T1499.004Application or System Exploitation

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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