CVE-2026-19667
Description
A flaw was found in bind9's named component. A remote attacker, by sending a specially crafted DNS negative answer of exactly 65536 bytes from an authoritative server, can cause a 16-bit length truncation. This results in a zero-byte negative cache entry. When named attempts to read this invalid entry, it will unexpectedly terminate, leading to a Denial of Service (DoS).
Statement
This is an Important denial of service flaw in BIND 9's named service. An attacker-controlled authoritative server can trigger a named abort by sending a precisely sized negative DNS answer. This vulnerability primarily affects BIND instances configured as recursive resolvers that query untrusted authoritative servers, leading to service disruption.
Mitigation
To reduce the exposure to this vulnerability, configure BIND 9 to forward all DNS queries to trusted, non-vulnerable upstream DNS servers. This prevents the local `named` instance from directly interacting with potentially malicious authoritative servers.
Example configuration in `named.conf`:
options {
forwarders { 192.0.2.1; 192.0.2.2; };
forward only;
};
Replace `192.0.2.1` and `192.0.2.2` with the IP addresses of your trusted upstream DNS servers. After modifying the configuration, restart the `named` service for the changes to take effect. This configuration may impact DNS resolution if the configured forwarders are unavailable or do not provide comprehensive resolution.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).
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)
Availability
Technical Impact: DoS: Crash, Exit, or Restart; DoS: Resource Consumption (Memory); DoS: Instability
This weakness can generally lead to undefined behavior and therefore crashes. When the calculated result is used for resource allocation, this weakness can cause too many (or too few) resources to be allocated, possibly enabling crashes if the product requests more resources than can be provided.
Integrity
Technical Impact: Modify Memory
If the value in question is important to data (as opposed to flow), simple data corruption has occurred. Also, if the overflow/wraparound results in other conditions such as buffer overflows, further memory corruption may occur.
Confidentiality,Availability,Access Control
Technical Impact: Execute Unauthorized Code or Commands; Bypass Protection Mechanism
This weakness can sometimes trigger buffer overflows, which can be used to execute arbitrary code. This is usually outside the scope of the product's implicit security policy.
Availability,Other
Technical Impact: Alter Execution Logic; DoS: Crash, Exit, or Restart; DoS: Resource Consumption (CPU)
If the overflow/wraparound occurs in a loop index variable, this could cause the loop to terminate at the wrong time - too early, too late, or not at all (i.e., infinite loops). With too many iterations, some loops could consume too many resources such as memory, file handles, etc., possibly leading to a crash or other DoS.
Access Control
Technical Impact: Bypass Protection Mechanism
If integer values are used in security-critical decisions, such as calculating quotas or allocation limits, integer overflows can be used to cause an incorrect security decision.
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