CVE-2019-25040Public exploit

Function hang via cyclic compression pointer

Published Apr 27, 2021 · Updated Aug 5, 2024

An infinite loop in dname_pkt_copy in NLnet Labs Unbound before 1.9.5 allows attackers to hang DNS-name copying via a compressed name. The routine follows a compression pointer back to packet offset zero without limiting pointer traversals, causing processing to restart indefinitely. The vendor disputes security impact because earlier packet parsing rejects unbounded pointers, leaving no remote or local path to the loop in a running installation.

CVSS severity7.5
High
EPSS probability1.99%
Next 30 days · Sep 16, 2026
Known exploitationUnconfirmed
Based on sourced intelligence
Hinoki checkNot available
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Summary

What happened

An infinite loop in dname_pkt_copy in NLnet Labs Unbound before 1.9.5 allows attackers to hang DNS-name copying via a compressed name. The routine follows a compression pointer back to packet offset zero without limiting pointer traversals, causing processing to restart indefinitely. The vendor disputes security impact because earlier packet parsing rejects unbounded pointers, leaving no remote or local path to the loop in a running installation.

The record

CVE
CVE-2019-25040
Published
Apr 27, 2021
Updated
Aug 5, 2024
Vendor
Unknown vendor
Product
Unknown product
Classifications
CWE-835, CWE-400
Attack vector
Unavailable
Privileges
Unavailable

Timeline

How it unfolded

  1. Apr 27, 2021CVE publishedPublication date reported by the CVE source.
  2. Aug 5, 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?

Affected buildAffected product and version details are unavailable.

What conditions does exploitation require?

Attack vectorUnavailable in this record.
Required privilegesUnavailable in this record.

What is affected?

Affected products and versions are unavailable in this record.

Published CVSS scores

7.5NIST National Vulnerability DatabaseCVSS:3.1/AV:N/AC:L/PR:N/UI:N/S:U/C:N/I:N/A:H
5.0NIST National Vulnerability DatabaseAV: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.

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)
VectorUnavailable
PrivilegesUnavailable
Known exploitationUnconfirmed
Public exploitPublished

Weakness, pattern, technique

CWE-835Loop with Unreachable Exit Condition ('Infinite Loop')
CWE-400Uncontrolled Resource Consumption ('Resource Exhaustion')

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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