CVE-2026-6949
Description
A flaw was found in Samba's internal DNS server when processing TSIG-signed DNS packets containing compressed names. Incorrect size calculations while determining the portion of the DNS packet covered by the TSIG signature can result in an integer underflow, leading to an out-of-bounds memory write during packet processing. A remote attacker can send a specially crafted TSIG-signed DNS packet to cause the DNS server to terminate unexpectedly.
Statement
Red Hat Product Security evaluates this vulnerability as having an Important impact for Samba deployments operating as an Active Directory Domain Controller (AD DC) using the internal DNS server engine.
Red Hat Enterprise Linux (RHEL) Context: Default installations of Red Hat Enterprise Linux (RHEL) are not affected. RHEL does not ship or support the Samba Active Directory Domain Controller (AD DC) role or its internal DNS server component where this vulnerability resides.
Additionally, Samba AD DC deployments that use the external BIND9 DLZ plugin instead of the internal DNS server engine are completely unaffected by this issue.
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 | N/A |
| Attack Vector | Network | N/A | N/A |
| Attack Complexity | Low | N/A | N/A |
| Privileges Required | None | N/A | N/A |
| User Interaction | None | N/A | N/A |
| Scope | Unchanged | N/A | N/A |
| Confidentiality | None | N/A | N/A |
| Integrity Impact | None | N/A | N/A |
| Availability Impact | High | N/A | N/A |
Vector
Red Hat: 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.
Acknowledgements
Red Hat would like to thank Arjun Basnet (Securin Labs) for reporting this issue.
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