CVE-2021-3448Network attack vector

DNS cache poisoning via fixed forwarding port

Published Apr 8, 2021 · Updated Dec 3, 2025

DNS cache poisoning in Simon Kelley dnsmasq before 2.85 allows remote attackers to forge cached replies via network DNS queries. When an upstream server is bound to a source interface or address, the forwarding path reuses one fixed UDP source port instead of selecting a random port per query. Exploitation requires learning that port, initiating a query, spoofing the upstream server, winning the reply race, and guessing the 16-bit transaction ID; accepted records redirect later DNS lookups.

CVSS severity4.0
Medium
EPSS probability2.29%
Next 30 days · Sep 16, 2026
Known exploitationUnconfirmed
Based on sourced intelligence
Hinoki checkNot available
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Summary

What happened

DNS cache poisoning in Simon Kelley dnsmasq before 2.85 allows remote attackers to forge cached replies via network DNS queries. When an upstream server is bound to a source interface or address, the forwarding path reuses one fixed UDP source port instead of selecting a random port per query. Exploitation requires learning that port, initiating a query, spoofing the upstream server, winning the reply race, and guessing the 16-bit transaction ID; accepted records redirect later DNS lookups.

The record

CVE
CVE-2021-3448
Published
Apr 8, 2021
Updated
Dec 3, 2025
Vendor
Simon Kelley
Product
dnsmasq
Classifications
CWE-358, T1557
Attack vector
network
Privileges
unauthenticated

Timeline

How it unfolded

  1. Apr 8, 2021CVE publishedPublication date reported by the CVE source.
  2. Dec 3, 2025Record 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=dnsmasq 2.85

What conditions does exploitation require?

Attack vectornetwork
Required privilegesunauthenticated

What is affected?

Simon Kelley · dnsmasqversion=dnsmasq 2.85

Published CVSS scores

4.0CISA-ADPCVSS:3.1/AV:N/AC:H/PR:N/UI:N/S:C/C:N/I:L/A:N
4.0NVDCVSS:3.1/AV:N/AC:H/PR:N/UI:N/S:C/C:N/I:L/A:N

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-358Improperly Implemented Security Check for Standard
T1557Adversary-in-the-Middle

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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