CVE-2023-3341: ISC BIND DNS Server DoS Vulnerability

CVE-2023-3341 Overview

CVE-2023-3341 is a stack exhaustion denial-of-service vulnerability in the Internet Systems Consortium (ISC) BIND 9 DNS server. The code that processes control channel messages sent to named calls certain functions recursively during packet parsing. Recursion depth is limited only by the maximum accepted packet size, allowing an unauthenticated attacker to exhaust available stack memory and terminate the named process. Because each incoming control channel message is fully parsed before authentication, exploitation does not require a valid Remote Name Daemon Control (RNDC) key. Only network access to the configured control channel TCP port is required, classifying this as both an out-of-bounds write [CWE-787] and an uncontrolled recursion [CWE-1325] flaw.

Critical Impact

Remote, unauthenticated attackers with network access to the named control channel port can crash the DNS server, disrupting name resolution for all dependent services.

Affected Products

• ISC BIND 9 versions 9.2.0 through 9.16.43, 9.18.0 through 9.18.18, and 9.19.0 through 9.19.16
• ISC BIND Supported Preview Edition versions 9.9.3-S1 through 9.16.43-S1 and 9.18.0-S1 through 9.18.18-S1
• Fedora 37 and 38, Debian Linux 10 and 11, and NetApp products bundling BIND

Discovery Timeline

• 2023-09-20 - CVE-2023-3341 published to the National Vulnerability Database (NVD)
• 2023-09-20 - ISC publishes CVE-2023-3341 Documentation and an Openwall OSS Security Discussion
• 2023-10-13 - NetApp publishes NetApp Security Advisory
• 2024-01 - Debian publishes Debian LTS Security Announcement
• 2025-12-02 - Last updated in the NVD database

Technical Details for CVE-2023-3341

Vulnerability Analysis

The BIND 9 named daemon exposes a control channel used by the rndc administrative utility. Messages received on this channel are parsed by recursive functions in the control channel handling code. The parser does not enforce a maximum recursion depth. An attacker can craft a deeply nested control message that forces named to recurse until the thread stack is exhausted, triggering a process abort and a denial-of-service condition for DNS resolution.

Root Cause

The defect resides in the packet-parsing code paths for control channel messages. The parser invokes itself recursively for each nested element in the incoming message, with recursion bounded only by the maximum accepted packet size rather than by an explicit depth limit. This pattern matches CWE-1325, improperly controlled sequential memory allocation, where untrusted input dictates stack growth.

Attack Vector

Exploitation requires only TCP connectivity to the port on which the control channel listens, typically TCP 953 on the loopback interface but frequently exposed to management networks. Because authentication occurs after full packet parsing, the attacker does not need a valid RNDC key or HMAC shared secret. A single malformed message of sufficient size is enough to terminate the named process. Restart-on-failure configurations may absorb individual crashes, but sustained traffic can keep the resolver offline.

No verified public proof-of-concept code is available. See the ISC CVE-2023-3341 Documentation for vendor-provided technical details.

Detection Methods for CVE-2023-3341

Indicators of Compromise

• Unexpected termination or repeated restarts of the named process with stack overflow or segmentation fault entries in syslog or systemd journal output
• Inbound TCP connections to the BIND control channel port (default 953) from hosts other than authorized management stations
• Abnormally large or malformed messages logged by the BIND control channel listener prior to a crash

Detection Strategies

• Monitor BIND log channels for named exit, assertion, or fatal errors correlated in time with control channel traffic
• Alert on TCP flows to port 953 originating outside the configured controls ACL
• Track DNS service availability metrics and trigger investigations when resolver downtime coincides with inbound control channel activity

Monitoring Recommendations

• Forward named logs and host process telemetry to a centralized logging or SIEM platform for correlation with network flow data
• Baseline normal control channel traffic patterns and flag deviations in source IP, packet size, or frequency
• Verify host integrity and patch level for BIND across all DNS servers, including hidden primaries and Supported Preview Edition deployments

How to Mitigate CVE-2023-3341

Immediate Actions Required

• Upgrade BIND 9 to a patched release: 9.16.44, 9.18.19, 9.19.17, or the corresponding Supported Preview Edition builds 9.16.44-S1 and 9.18.19-S1
• Restrict the controls statement in named.conf so the control channel listens only on loopback or trusted management interfaces
• Apply distribution updates referenced in the Debian Security Advisory DSA-5504 and the Fedora package announcements

Patch Information

ISC released fixed versions concurrently with the advisory. Operators running ISC BIND should upgrade to 9.16.44, 9.18.19, or 9.19.17. Subscribers to the Supported Preview Edition should move to 9.16.44-S1 or 9.18.19-S1. Distribution-specific packages are available through the Fedora Package Announcement and the Debian LTS Security Announcement. NetApp customers should consult the NetApp Security Advisory for product-specific guidance.

Workarounds

• Bind the control channel to 127.0.0.1 and use firewall rules to block external access to TCP port 953
• Disable the control channel entirely by removing or commenting the controls statement when rndc administration is not required
• Enforce network segmentation so only designated management hosts can reach DNS server administrative ports