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HIGH

A buffer overrun in lease file parsing code can be used to exploit a common vulnerability shared by dhcpd and dhclient

Published May 26, 2021

Description

In ISC DHCP 4.1-ESV-R1 -> 4.1-ESV-R16, ISC DHCP 4.4.0 -> 4.4.2 (Other branches of ISC DHCP (i.e., releases in the 4.0.x series or lower and releases in the 4.3.x series) are beyond their End-of-Life (EOL) and no longer supported by ISC. From inspection it is clear that the defect is also present in releases from those series, but they have not been officially tested for the vulnerability), The outcome of encountering the defect while reading a lease that will trigger it varies, according to: the component being affected (i.e., dhclient or dhcpd) whether the package was built as a 32-bit or 64-bit binary whether the compiler flag -fstack-protection-strong was used when compiling In dhclient, ISC has not successfully reproduced the error on a 64-bit system. However, on a 32-bit system it is possible to cause dhclient to crash when reading an improper lease, which could cause network connectivity problems for an affected system due to the absence of a running DHCP client process. In dhcpd, when run in DHCPv4 or DHCPv6 mode: if the dhcpd server binary was built for a 32-bit architecture AND the -fstack-protection-strong flag was specified to the compiler, dhcpd may exit while parsing a lease file containing an objectionable lease, resulting in lack of service to clients. Additionally, the offending lease and the lease immediately following it in the lease database may be improperly deleted. if the dhcpd server binary was built for a 64-bit architecture OR if the -fstack-protection-strong compiler flag was NOT specified, the crash will not occur, but it is possible for the offending lease and the lease which immediately followed it to be improperly deleted.

Affected products

Remediation

Vendor solution

Upgrade to the patched release most closely related to your current version of ISC DHCP:

ISC DHCP 4.1-ESV-R16-P1 ISC DHCP 4.4.2-P1

Red Hat statement

To abuse this flaw an attacker has to be on the same local sub-net of the victim machine. An attacker may send crafted DHCP messages with long lease statements that, when stored locally on file and then re-read by dhclient or dhcpd, might trigger the bug.

Metrics

Weaknesses (1)

CWE-119

Buffer Overflow

References (13)

Change history (0)

No recorded changes yet.

Sources
CVE.org / MITRE
Status PUBLISHED
Assigner isc
Published May 26, 2021
Updated Sep 16, 2024
Reserved Jan 15, 2021
Link CVE-2021-25217
CISA Vulnrichment
Updated n/a
NVD
Status Modified
Modified Jun 17, 2026
Link CVE-2021-25217
Red Hat
Severity Important
Public date May 26, 2021
Links CVE-2021-25217 - Bugzilla