CVE-2020-25683Network attack vector

Remote crash via negative-size DNSSEC copy

Published Jan 20, 2021 · Updated Nov 4, 2025

Heap-based buffer overflow in dnsmasq before 2.83 allows remote attackers to crash the service via crafted DNS replies. Missing length checks in rfc1035.c extract_name let get_rdata call memcpy with a negative size while parsing unvalidated DNSSEC records. DNSSEC must be compiled and enabled, and remote attackers must control an upstream DNS server or inject an accepted reply.

CVSS severity5.9
Medium
EPSS probability86.04%
Next 30 days · Sep 16, 2026
Known exploitationUnconfirmed
Based on sourced intelligence
Hinoki checkNot available
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Summary

What happened

Heap-based buffer overflow in dnsmasq before 2.83 allows remote attackers to crash the service via crafted DNS replies. Missing length checks in rfc1035.c extract_name let get_rdata call memcpy with a negative size while parsing unvalidated DNSSEC records. DNSSEC must be compiled and enabled, and remote attackers must control an upstream DNS server or inject an accepted reply.

The record

CVE
CVE-2020-25683
Published
Jan 20, 2021
Updated
Nov 4, 2025
Vendor
Simon Kelley
Product
dnsmasq
Classifications
CWE-122, T1499
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

7.1NIST NVDAV:N/AC:M/Au:N/C:N/I:N/A:C
5.9NIST NVDCVSS:3.1/AV:N/AC:H/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 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-122Heap-based Buffer Overflow
T1499Endpoint Denial of Service

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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