CVE-2019-6477 (GCVE-0-2019-6477)

Vulnerability from cvelistv5 – Published: 2019-11-26 16:11 – Updated: 2024-09-16 16:47
VLAI
Title
TCP-pipelined queries can bypass tcp-clients limit
Summary
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).
Severity
7.5 (High)
CVSS:3.1/AV:N/AC:L/PR:N/UI:N/S:U/C:N/I:N/A:H
CWE
  • By design, BIND is intended to limit the number of TCP clients that can be connected at any given time. The update to this functionality introduced by CVE-2018-5743 changed how BIND calculates the number of concurrent TCP clients from counting the outstanding TCP queries to counting the TCP client connections. On a server with TCP-pipelining capability, it is possible for one TCP client to send a large number of DNS requests over a single connection. Each outstanding query will be handled internally as an independent client request, thus bypassing the new TCP clients limit. 9.11.6-P1 -> 9.11.12, 9.12.4-P1 -> 9.12.4-P2, 9.14.1 -> 9.14.7, and versions 9.11.5-S6 -> 9.11.12-S1 of BIND 9 Supported Preview Edition. Versions 9.15.0 -> 9.15.5 of the BIND 9.15 development branch are also affected.
Assigner
isc CNA under the mitre root
CNA scorecard A 95/100 over 33 records in the last 180 days details
References
Impacted products
Vendor Product Version CPE status
ISC BIND9 Affected: 9.11.6-P1 -> 9.11.12, 9.12.4-P1 -> 9.12.4-P2, 9.14.1 -> 9.14.7, and versions 9.11.5-S6 -> 9.11.12-S1 of BIND 9 Supported Preview Edition. Versions 9.15.0 -> 9.15.5 of the BIND 9.15 development branch are also affected
guessed Create a notification for this product.
Date Public
2019-11-20 00:00
Show details on NVD website
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Solutions

CNA · isc
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.

Workarounds

CNA · isc
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.

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Sightings

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Nomenclature

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Vulnerability timeline

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