CVE-2026-6507
Description
A flaw was found in dnsmasq. A remote attacker could exploit an out-of-bounds write vulnerability by sending a specially crafted BOOTREPLY (Bootstrap Protocol Reply) packet to a dnsmasq server configured with the --dhcp-split-relay option. This can lead to memory corruption, causing the dnsmasq daemon to crash and resulting in a denial of service (DoS).
Statement
This vulnerability is rated Moderate rather than Important because exploitation is limited to a service crash and requires a non-standard configuration that is not enabled by default. The issue only affects dnsmasq instances explicitly configured to act as a DHCP split relay via the dhcp-split-relay option. Systems running dnsmasq with default settings, local DNS caching, or standard DHCP server roles are not susceptible to this flaw.
Mitigation
To mitigate this issue, ensure that the `dnsmasq` service is not configured with the `--dhcp-split-relay` option. If this option is currently in use, remove it from the `dnsmasq` configuration. After modifying the configuration, the `dnsmasq` service must be restarted for the changes to take effect. This may temporarily interrupt DHCP and DNS services provided by `dnsmasq`.
Common Vulnerability Scoring System (CVSS) Score Details
Info alert:Important note
CVSS scores for open source components depend on vendor-specific factors (e.g. version or build chain). Therefore, Red Hat's score and impact rating can be different from NVD and other vendors. Red Hat remains the authoritative CVE Naming Authority (CNA) source for its products and services (see Red Hat classifications).
The following CVSS metrics and score provided are preliminary and subject to review.
CVSS v3 Score Breakdown
| Red Hat | NVD | cve.org | |
|---|---|---|---|
| Base Score | 7.5 | N/A | 7.5 |
| Attack Vector | Network | N/A | Network |
| Attack Complexity | Low | N/A | Low |
| Privileges Required | None | N/A | None |
| User Interaction | None | N/A | None |
| Scope | Unchanged | N/A | Unchanged |
| Confidentiality | None | N/A | None |
| Integrity Impact | None | N/A | None |
| Availability Impact | High | N/A | High |
Vector
Red Hat: CVSS:3.1/AV:N/AC:L/PR:N/UI:N/S:U/C:N/I:N/A:H
cve.org: CVSS:3.1/AV:N/AC:L/PR:N/UI:N/S:U/C:N/I:N/A:H
Understanding the Weakness (CWE)
Integrity
Technical Impact: Modify Memory; Execute Unauthorized Code or Commands
Write operations could cause memory corruption. In some cases, an adversary can modify control data such as return addresses in order to execute unexpected code.
Availability
Technical Impact: DoS: Crash, Exit, or Restart
Attempting to access out-of-range, invalid, or unauthorized memory could cause the product to crash.
Other
Technical Impact: Unexpected State
Subsequent write operations can produce undefined or unexpected results.
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