CVE-2021-25217

Service interruption and lease deletion via option parsing

Published May 26, 2021 · Updated Sep 16, 2024

Buffer overrun in ISC DHCP 4.1-ESV-R1 through 4.1-ESV-R16 and 4.4.0 through 4.4.2 allows remote attackers to interrupt service via crafted leases. The stored-lease parser handles encapsulated option data differently from the wire parser, overrunning a buffer when dhcpd or dhclient rereads a crafted lease. A 32-bit dhclient can crash; dhcpd exits only when built for 32-bit with strong stack protection, while other dhcpd builds can delete the crafted lease and the following lease.

CVSS severity7.4
High
EPSS probability6.12%
Next 30 days · Sep 16, 2026
Known exploitationUnconfirmed
Based on sourced intelligence
Hinoki checkNot available
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Summary

What happened

Buffer overrun in ISC DHCP 4.1-ESV-R1 through 4.1-ESV-R16 and 4.4.0 through 4.4.2 allows remote attackers to interrupt service via crafted leases. The stored-lease parser handles encapsulated option data differently from the wire parser, overrunning a buffer when dhcpd or dhclient rereads a crafted lease. A 32-bit dhclient can crash; dhcpd exits only when built for 32-bit with strong stack protection, while other dhcpd builds can delete the crafted lease and the following lease.

The record

CVE
CVE-2021-25217
Published
May 26, 2021
Updated
Sep 16, 2024
Vendor
Internet Systems Consortium
Product
ISC DHCP
Classifications
CWE-119, T1499.004
Attack vector
adjacent
Privileges
unauthenticated

Timeline

How it unfolded

  1. May 26, 2021CVE publishedPublication date reported by the CVE source.
  2. Sep 16, 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?

Compare these published version ranges with your installed build and any vendor patches.

  1. Affected versionversion=4.1 ESV <4.1-ESV-R16-P1
  2. Affected versionversion=4.4 <4.4.2-P1

What conditions does exploitation require?

Attack vectoradjacent
Required privilegesunauthenticated

What is affected?

Internet Systems Consortium · ISC DHCPversion=4.1 ESV <4.1-ESV-R16-P1; version=4.4 <4.4.2-P1

Published CVSS scores

7.4Internet Systems ConsortiumCVSS:3.1/AV:A/AC:L/PR:N/UI:N/S:C/C:N/I:N/A:H
3.3NIST National Vulnerability DatabaseAV:A/AC:L/Au:N/C:N/I:N/A:P
6.5Internet Systems ConsortiumCVSS:3.1/AV:A/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.

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)
Vectoradjacent
Privilegesunauthenticated
Known exploitationUnconfirmed
Public exploitUnconfirmed

Weakness, pattern, technique

CWE-119Improper Restriction of Operations within the Bounds of a Memory Buffer
T1499.004Endpoint Denial of Service: Application or System Exploitation

Public exploit references

No public exploit references are available in this record.

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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