CVE-2019-25036Public exploit

Resolver abort via unchecked DNAME length relationship

Published Apr 27, 2021 · Updated Aug 5, 2024

Reachable assertion in Unbound before 1.9.5 causes a resolver crash when synth_cname processes an invalid DNS packet. The function assumes the query name is longer than the DNAME owner, then asserts that relationship before subtracting their lengths to form the alias offset. NLnet Labs disputes vulnerability status because a running installation cannot be driven into this state remotely or locally, limiting the documented consequence to the audit test path.

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

Reachable assertion in Unbound before 1.9.5 causes a resolver crash when synth_cname processes an invalid DNS packet. The function assumes the query name is longer than the DNAME owner, then asserts that relationship before subtracting their lengths to form the alias offset. NLnet Labs disputes vulnerability status because a running installation cannot be driven into this state remotely or locally, limiting the documented consequence to the audit test path.

The record

CVE
CVE-2019-25036
Published
Apr 27, 2021
Updated
Aug 5, 2024
Vendor
Unknown vendor
Product
Unknown product
Classifications
CWE-617
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

5.0NIST NVDAV:N/AC:L/Au:N/C:N/I:N/A:P
7.5NIST NVDCVSS:3.1/AV:N/AC:L/PR:N/UI:N/S:U/C:N/I:N/A:H
5.3SUSECVSS:3.1/AV:N/AC:L/PR:N/UI:N/S:U/C:N/I:N/A:L

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 9, 2026Sep 15, 2026
Latest reporting daySep 15, 2026
Latest daily unique IPsUnavailable
Prior 30-day averageUnavailable
SourceShadowserver honeypots (KEV)
VectorUnavailable
PrivilegesUnavailable
Known exploitationUnconfirmed
Public exploitPublished

Weakness, pattern, technique

CWE-617Reachable Assertion

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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