CVE-2023-3341: ISC BIND Denial of Service Vulnerability

CVE-2023-3341 Overview

A stack exhaustion vulnerability exists in ISC BIND's control channel message processing that allows remote attackers to cause a denial of service condition. The code responsible for parsing control channel messages sent to named utilizes recursive function calls without adequate depth limiting. Since recursion depth is constrained only by the maximum accepted packet size, an attacker can craft malicious packets that exhaust available stack memory, causing the named process to terminate unexpectedly.

Critically, this vulnerability can be exploited without valid authentication credentials. Each incoming control channel message is fully parsed before its contents are authenticated, meaning attackers only require network access to the control channel's configured TCP port to exploit this flaw—no valid RNDC key is necessary.

Critical Impact

Remote unauthenticated attackers can crash BIND DNS servers by sending specially crafted packets to the control channel, causing complete DNS service disruption without requiring valid RNDC authentication keys.

Affected Products

• ISC BIND 9.2.0 through 9.16.43
• ISC BIND 9.18.0 through 9.18.18
• ISC BIND 9.19.0 through 9.19.16
• ISC BIND 9.9.3-S1 through 9.16.43-S1 (Supported Preview Edition)
• ISC BIND 9.18.0-S1 through 9.18.18-S1 (Supported Preview Edition)
• Fedora 37 and 38
• Debian Linux 10.0 and 11.0

Discovery Timeline

• 2023-09-20 - CVE-2023-3341 published to NVD
• 2025-12-02 - Last updated in NVD database

Technical Details for CVE-2023-3341

Vulnerability Analysis

This vulnerability (CWE-787: Out-of-bounds Write, CWE-1325: Improperly Controlled Sequential Memory Allocation) resides in BIND's control channel packet parsing logic. The named daemon provides a remote management interface through the control channel, typically accessed via the rndc utility. When processing incoming messages on this channel, the parsing code employs recursive function calls to handle nested data structures within the packet.

The fundamental flaw is the absence of explicit recursion depth limits during packet parsing. The only constraint on recursion depth is the maximum packet size that BIND will accept. An attacker can construct a deeply nested packet structure that, while technically valid in terms of size, triggers excessive recursive calls that consume stack memory until it is exhausted.

Root Cause

The root cause stems from improper sequential memory allocation during recursive parsing operations. The parsing functions call themselves recursively for each level of nesting in the control channel message structure. Without explicit bounds checking on recursion depth, the stack frame allocations for each recursive call accumulate until the available stack space is exhausted. This design oversight allows the maximum packet size (a network-level constraint) to indirectly control stack usage (a process-level resource), creating a resource exhaustion condition.

Attack Vector

The attack can be executed remotely over the network by any attacker who can reach the control channel's TCP port (default port 953). The attack is particularly dangerous because:

1. No authentication required: The vulnerable parsing code executes before any authentication checks occur
2. Low complexity: The attacker simply needs to send a malformed packet with excessive nesting
3. No user interaction: The attack is fully automated and requires no victim action
4. Immediate impact: Successful exploitation causes immediate named process termination

An attacker would craft a control channel message containing deeply nested structures, send it to the target BIND server's control channel port, and the recursive parsing would exhaust stack memory, triggering process termination. The attack can be repeated to maintain the denial of service condition even after automatic service restart.

Detection Methods for CVE-2023-3341

Indicators of Compromise

• Unexpected named process crashes or restarts, particularly correlating with network activity on the control channel port
• System logs showing segmentation faults or stack overflow errors from the named process
• Unusual network connections or traffic patterns to TCP port 953 (default RNDC control channel)
• Core dumps from named indicating stack exhaustion conditions

Detection Strategies

• Monitor for named process crashes using process monitoring tools and correlate with network activity logs
• Implement network intrusion detection rules to identify anomalous traffic to the control channel port (TCP 953)
• Review system logs for stack overflow or memory exhaustion errors related to the BIND daemon
• Deploy packet inspection to detect unusually large or malformed control channel messages

Monitoring Recommendations

• Configure alerting on named service restarts or unexpected terminations
• Implement network flow monitoring for the control channel port to detect scanning or attack attempts
• Use SentinelOne Singularity platform to monitor for process crashes and anomalous network behavior
• Establish baseline metrics for control channel traffic volume to identify deviations

How to Mitigate CVE-2023-3341

Immediate Actions Required

• Update ISC BIND to version 9.16.44, 9.18.19, or 9.19.17 (or corresponding -S versions for Supported Preview Edition)
• Restrict network access to the control channel port using firewall rules to limit exposure
• Apply operating system vendor patches from Debian, Fedora, or other distributions as available
• Monitor BIND servers for unexpected crashes while planning upgrade windows

Patch Information

ISC has released patched versions that address this vulnerability by implementing proper recursion depth limits in the control channel parsing code. Organizations should update to the following versions:

• BIND 9.16.44 or later (for 9.16.x branch)
• BIND 9.18.19 or later (for 9.18.x branch)
• BIND 9.19.17 or later (for 9.19.x development branch)
• BIND 9.16.44-S1 or later (Supported Preview Edition)
• BIND 9.18.19-S1 or later (Supported Preview Edition)

Refer to the ISC Knowledge Base CVE-2023-3341 for official patch details. Linux distribution users should apply security updates from Debian Security Advisory DSA-5504, the Fedora Package Announcements, or their respective distribution's security update channels.

Workarounds

• Restrict access to the control channel by binding it to localhost only if remote management is not required
• Implement strict firewall rules to limit control channel access to trusted management hosts only
• Consider disabling the control channel entirely if RNDC functionality is not needed in your environment
• Deploy network segmentation to isolate DNS servers and limit exposure of management interfaces

# Configuration example - Restrict control channel to localhost only
# Add to named.conf:
controls {
    inet 127.0.0.1 port 953
        allow { 127.0.0.1; } keys { "rndc-key"; };
};

# Or disable control channel entirely if not needed:
controls { };