CVE-2023-31137Public exploitNetwork attack vector

Remote service crash via TXT record underflow

Published May 9, 2023 · Updated Feb 13, 2025

Integer underflow in MaraDNS 3.5.0024 and earlier allows remote attackers to crash the DNS service via a crafted TXT answer. In decomp_get_rddata, a TXT Answer RR whose declared length is shorter than its data produces a negative length that decomp_append_bytes converts into an enormous allocation. No authentication or user interaction is required; one crafted DNS packet can terminate the server and interrupt DNS service.

CVSS severity7.5
High
EPSS probability1.14%
Next 30 days · Sep 16, 2026
Known exploitationUnconfirmed
Based on sourced intelligence
Hinoki checkNot available
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Summary

What happened

Integer underflow in MaraDNS 3.5.0024 and earlier allows remote attackers to crash the DNS service via a crafted TXT answer. In decomp_get_rddata, a TXT Answer RR whose declared length is shorter than its data produces a negative length that decomp_append_bytes converts into an enormous allocation. No authentication or user interaction is required; one crafted DNS packet can terminate the server and interrupt DNS service.

The record

CVE
CVE-2023-31137
Published
May 9, 2023
Updated
Feb 13, 2025
Vendor
Sam Trenholme
Product
MaraDNS
Classifications
CWE-191, T1499.004
Attack vector
network
Privileges
unauthenticated

Timeline

How it unfolded

  1. May 9, 2023CVE publishedPublication date reported by the CVE source.
  2. Feb 13, 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=<= 3.5.0024

What conditions does exploitation require?

Attack vectornetwork
Required privilegesunauthenticated

What is affected?

Sam Trenholme · MaraDNSversion=<= 3.5.0024

Published CVSS scores

7.5GitHubCVSS: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 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-191Integer Underflow (Wrap or Wraparound)
T1499.004Application or System Exploitation

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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