CVE-2021-20213Network attack vector

Proxy crash via failed destination error handling

Published Mar 25, 2021 · Updated Aug 3, 2024

NULL pointer dereference in Privoxy before 3.0.29 allows remote attackers to crash the proxy through an intercepted HTTP request. When Host-based destination extraction and a subsequent allocation both fail, the intercepted-request path dereferences a null pointer. The nondefault accept-intercepted-requests setting must be enabled, and exploitation interrupts the proxy without reported data exposure.

CVSS severity7.5
High
EPSS probability1.57%
Next 30 days · Sep 16, 2026
Known exploitationUnconfirmed
Based on sourced intelligence
Hinoki checkNot available
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Summary

What happened

NULL pointer dereference in Privoxy before 3.0.29 allows remote attackers to crash the proxy through an intercepted HTTP request. When Host-based destination extraction and a subsequent allocation both fail, the intercepted-request path dereferences a null pointer. The nondefault accept-intercepted-requests setting must be enabled, and exploitation interrupts the proxy without reported data exposure.

The record

CVE
CVE-2021-20213
Published
Mar 25, 2021
Updated
Aug 3, 2024
Vendor
Privoxy Developers
Product
Privoxy
Classifications
CWE-476, T1499
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

7.5NIST NVDCVSS:3.1/AV:N/AC:L/PR:N/UI:N/S:U/C:N/I:N/A:H
4.3NIST NVDAV:N/AC:M/Au:N/C:N/I:N/A:P
7.5Canonical Ubuntu SecurityCVSS: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.

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No observations available

Sep 9, 2026Sep 15, 2026
Latest reporting daySep 15, 2026
Latest daily unique IPsUnavailable
Prior 30-day averageUnavailable
SourceShadowserver honeypots (KEV)
Vectornetwork
Privilegesunauthenticated
Known exploitationUnconfirmed
Public exploitUnconfirmed

Weakness, pattern, technique

CWE-476NULL Pointer Dereference
T1499Endpoint Denial of Service

Public exploit references

No public exploit references are available in this record.

Labels summarize the accepted research assessment. They do not indicate a test against your environment.

Technologies

Your stack

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Your stack

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