CVE-2020-25685Public exploitNetwork attack vector

DNS cache poisoning via weak reply hashing

Published Jan 20, 2021 · Updated Nov 4, 2025

DNS cache poisoning in Simon Kelley dnsmasq before 2.83 allows remote attackers to redirect clients via forged DNS replies. In forward.c:reply_query(), reply matching relies only on a query-name hash using CRC32 without DNSSEC or SHA-1 with DNSSEC, allowing colliding names to reduce the guesses needed for acceptance. Exploitation requires a client to issue many queries for attacker-chosen domains; accepted replies poison the default-enabled cache and return false addresses to its clients.

CVSS severity3.7
Low
EPSS probability2.18%
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 2.83 allows remote attackers to redirect clients via forged DNS replies. In forward.c:reply_query(), reply matching relies only on a query-name hash using CRC32 without DNSSEC or SHA-1 with DNSSEC, allowing colliding names to reduce the guesses needed for acceptance. Exploitation requires a client to issue many queries for attacker-chosen domains; accepted replies poison the default-enabled cache and return false addresses to its clients.

The record

CVE
CVE-2020-25685
Published
Jan 20, 2021
Updated
Nov 4, 2025
Vendor
Simon Kelley
Product
dnsmasq
Classifications
CWE-326, T1565.002
Attack vector
network
Privileges
unauthenticated

Timeline

How it unfolded

  1. Jan 20, 2021CVE publishedPublication date reported by the CVE source.
  2. Nov 4, 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 2.83

What conditions does exploitation require?

Attack vectornetwork
Required privilegesunauthenticated

What is affected?

Simon Kelley · dnsmasqversion=dnsmasq 2.83

Published CVSS scores

4.3NVDAV:N/AC:M/Au:N/C:N/I:P/A:N
3.7NVDCVSS:3.1/AV:N/AC:H/PR:N/UI:N/S:U/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.

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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 exploitPublished

Weakness, pattern, technique

CWE-326Inadequate Encryption Strength
T1565.002Transmitted Data Manipulation

Public exploit references

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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