CVE-2019-6477
With pipelining enabled each incoming query on a TCP connection requires a similar resource allocation to a query received via UDP or via TCP without pipelining enabled. A client using a TCP-pipelined connection to a server could consume more resources than the server has been provisioned to handle. When a TCP connection with a large number of pipelined queries is closed, the load on the server releasing these multiple resources can cause it to become unresponsive, even for queries that can be answered authoritatively or from cache. (This is most likely to be perceived as an intermittent server problem).
- Isc Bind
- ≤ 9.11.12, 9.14.7, 9.15.5, 9.11.5, 9.11.6, 9.12.4
- CVSS 3.1
- 7.5 HIGH
- EPSS
- 4.1% (90th percentile)
- Weakness
- CWE-400
- NVD status
- Modified
- Published
- 2019-11-26
Fix
Upgrade to the patched release most closely related to your current version of BIND: BIND 9.11.13 BIND 9.14.8 BIND 9.15.6 BIND Supported Preview Edition is a special feature preview branch of BIND provided to eligible ISC support customers. BIND 9.11.13-S1 Note that the fix for CVE-2019-6477 addresses only the server memory leak issue. TCP-pipelining may still malfunction by dropping some responses on a TCP connection where a client query pattern generates excessive outstanding queries, but the malfunction will affect that TCP connection alone and will not cause any degradation of service to other clients. An affected client connection might also appear to hang, but will clear when either the client or the server initiates a close or reset and will not remain in that state indefinitely. Disabling TCP-pipelining entirely is completely effective at mitigating the vulnerability with minimal impact to clients that use pipelined TCP connections and with no impact to clients that do not support TCP-pipelining. The majority of Internet client DNS queries are transported over UDP or TCP without use of TCP-pipelining.
Workaround
The vulnerability can be avoided by disabling server TCP-pipelining: keep-response-order { any; }; and then restarting BIND. The server restart is necessary because neither a 'reload' nor a 'reconfig' operation will properly reset currently pipelining TCP clients.
No indexed exploits for CVE-2019-6477 yet
Our index is partial: it proves presence, never absence
No exploit for CVE-2019-6477 has been indexed yet. Our index is built from live traffic and upstream syncs, so this page can only say what it knows — not that no exploit exists.