CVE-2021-20274Network attack vector

Proxy crash via absent SOCKS5 credentials

Published Mar 9, 2021 · Updated Aug 3, 2024

NULL-pointer dereference in Privoxy before 3.0.32 allows remote attackers controlling its configured SOCKS5 server to crash the proxy. The socks5_connect() function tries to send a username and password after a SOCKS5 authentication response even when no credentials are configured, dereferencing a null pointer. Reachability requires use of an attacker-controlled or misbehaving SOCKS5 upstream, and the demonstrated consequence is interruption of the Privoxy service.

CVSS severity7.5
High
EPSS probability1.92%
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 3.0.32 allows remote attackers controlling its configured SOCKS5 server to crash the proxy. The socks5_connect() function tries to send a username and password after a SOCKS5 authentication response even when no credentials are configured, dereferencing a null pointer. Reachability requires use of an attacker-controlled or misbehaving SOCKS5 upstream, and the demonstrated consequence is interruption of the Privoxy service.

The record

CVE
CVE-2021-20274
Published
Mar 9, 2021
Updated
Aug 3, 2024
Vendor
Privoxy Developers
Product
Privoxy
Classifications
CWE-476, T1499.004
Attack vector
network
Privileges
unauthenticated

Timeline

How it unfolded

  1. Mar 9, 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 3.0.32

What conditions does exploitation require?

Attack vectornetwork
Required privilegesunauthenticated

What is affected?

Privoxy Developers · Privoxyversion=privoxy 3.0.32

Published CVSS scores

7.5NVDCVSS:3.1/AV:N/AC:L/PR:N/UI:N/S:U/C:N/I:N/A:H
5.0NVDAV:N/AC:L/Au:N/C:N/I:N/A:P

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 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-476NULL Pointer Dereference
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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