CVE-2019-6477 [High] | Denial of Service in Bind

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).

#	Date	Old EPSS score	New EPSS score	Delta (New - Old)
1	2026-06-15	5.68%	4.02%	-1.66%
2	2025-11-21	18.98%	5.68%	-13.29%
3	2025-11-18	—	18.98%	—

Date

Old EPSS score

New EPSS score

Delta (New - Old)

2026-06-15

5.68%

4.02%

-1.66%

2025-11-21

18.98%

5.68%

-13.29%

2025-11-18

—

18.98%

—

Base score	Version	Severity	Vector	Exploitability	Impact	Score source
7.5	3.1	HIGH	`CVSS:3.1/AV:N/AC:L/PR:N/UI:N/S:U/C:N/I:N/A:H` Click to expand Attack vector (AV:N) Could be attacked over the internet or any normal routed network—not just someone sitting at the machine. Attack complexity (AC:L) Once they can reach the bug, pulling it off is straightforward—no weird race conditions or rare setup. Privileges required (PR:N) No account or special rights needed—anonymous or random user is enough. User interaction (UI:N) Nobody has to click “OK” or open a trap file; it can work without a victim helping. Scope (S:U) Damage stays in the same “trust bubble” as the broken component—no big spill into unrelated systems. Confidentiality (C:N) Doesn’t really leak secrets in a meaningful way. Integrity (I:N) Data isn’t meaningfully altered or forged. Availability (A:H) Could take the service down hard or make it unusable for people who depend on it.	3.9	3.6	[email protected]
7.5	3.1	HIGH	`CVSS:3.1/AV:N/AC:L/PR:N/UI:N/S:U/C:N/I:N/A:H` Click to expand Attack vector (AV:N) Could be attacked over the internet or any normal routed network—not just someone sitting at the machine. Attack complexity (AC:L) Once they can reach the bug, pulling it off is straightforward—no weird race conditions or rare setup. Privileges required (PR:N) No account or special rights needed—anonymous or random user is enough. User interaction (UI:N) Nobody has to click “OK” or open a trap file; it can work without a victim helping. Scope (S:U) Damage stays in the same “trust bubble” as the broken component—no big spill into unrelated systems. Confidentiality (C:N) Doesn’t really leak secrets in a meaningful way. Integrity (I:N) Data isn’t meaningfully altered or forged. Availability (A:H) Could take the service down hard or make it unusable for people who depend on it.	3.9	3.6	[email protected]
5.0	2.0	MEDIUM	`AV:N/AC:L/Au:N/C:N/I:N/A:P` Click to expand Access vector (AV:N) Can be exploited remotely over network reachability. Access complexity (AC:L) Exploitation conditions are straightforward and predictable. Authentication (AU:N) No authentication is required. Confidentiality impact (C:N) No confidentiality impact. Integrity impact (I:N) No integrity impact. Availability impact (A:P) Partial availability impact.	10.0	2.9	[email protected]

Base score

Version

Severity

Vector

Exploitability

Impact

Score source

7.5

3.1

HIGH

CVSS:3.1/AV:N/AC:L/PR:N/UI:N/S:U/C:N/I:N/A:H Click to expand

Attack vector (AV:N): Could be attacked over the internet or any normal routed network—not just someone sitting at the machine.
Attack complexity (AC:L): Once they can reach the bug, pulling it off is straightforward—no weird race conditions or rare setup.
Privileges required (PR:N): No account or special rights needed—anonymous or random user is enough.
User interaction (UI:N): Nobody has to click “OK” or open a trap file; it can work without a victim helping.
Scope (S:U): Damage stays in the same “trust bubble” as the broken component—no big spill into unrelated systems.
Confidentiality (C:N): Doesn’t really leak secrets in a meaningful way.
Integrity (I:N): Data isn’t meaningfully altered or forged.
Availability (A:H): Could take the service down hard or make it unusable for people who depend on it.

3.9

3.6

[email protected]

7.5

3.1

HIGH

CVSS:3.1/AV:N/AC:L/PR:N/UI:N/S:U/C:N/I:N/A:H Click to expand

Attack vector (AV:N): Could be attacked over the internet or any normal routed network—not just someone sitting at the machine.
Attack complexity (AC:L): Once they can reach the bug, pulling it off is straightforward—no weird race conditions or rare setup.
Privileges required (PR:N): No account or special rights needed—anonymous or random user is enough.
User interaction (UI:N): Nobody has to click “OK” or open a trap file; it can work without a victim helping.
Scope (S:U): Damage stays in the same “trust bubble” as the broken component—no big spill into unrelated systems.
Confidentiality (C:N): Doesn’t really leak secrets in a meaningful way.
Integrity (I:N): Data isn’t meaningfully altered or forged.
Availability (A:H): Could take the service down hard or make it unusable for people who depend on it.

3.9

3.6

[email protected]

5.0

2.0

MEDIUM

AV:N/AC:L/Au:N/C:N/I:N/A:P Click to expand

Access vector (AV:N): Can be exploited remotely over network reachability.
Access complexity (AC:L): Exploitation conditions are straightforward and predictable.
Authentication (AU:N): No authentication is required.
Confidentiality impact (C:N): No confidentiality impact.
Integrity impact (I:N): No integrity impact.
Availability impact (A:P): Partial availability impact.

10.0

2.9

[email protected]

OS Trackers for CVE-2019-6477

vendor	priority	summary	link
`alpine`	high	CVE-2019-6477: 1 source package rows (bind); 25 state rows across 10 repos (3.10-main, 3.11-main, 3.12-main, 3.17-main, 3.18-main, 3.19-main, 3.20-main, 3.21-main, 3.22-main, edge-main); fixed 10, open 15.	https://security.alpinelinux.org/vuln/CVE-2019-6477
`debian`	not yet assigned	CVE-2019-6477 not yet assigned priority: Debian including 1 source packages (bind9), 5 status rows across 5 suites (bookworm, bullseye, forky, sid, trixie): resolved 5.	https://security-tracker.debian.org/tracker/CVE-2019-6477
`redhat`	medium	—	https://access.redhat.com/security/cve/CVE-2019-6477
`ubuntu`	medium	CVE-2019-6477 medium priority: Ubuntu including 1 source packages (bind9), 6 status rows across 6 suites (bionic, disco, eoan, trusty, upstream, xenial): released 3, not-affected 2, needs-triage 1.	https://ubuntu.com/security/CVE-2019-6477

Affected software / configurations for CVE-2019-6477

Vendor	Product	Version	Raw CPE
isc	bind	>= 9.11.7, <= 9.11.12	cpe:2.3:a:isc:bind::::::::
isc	bind	>= 9.14.1, <= 9.14.7	cpe:2.3:a:isc:bind::::::::
isc	bind	>= 9.15.0, <= 9.15.5	cpe:2.3:a:isc:bind::::::::
isc	bind	9.11.5	cpe:2.3:a:isc:bind:9.11.5:s6:::supported_preview:::*
isc	bind	9.11.6	cpe:2.3:a:isc:bind:9.11.6:p1::::::
isc	bind	9.11.6	cpe:2.3:a:isc:bind:9.11.6:rc1::::::
isc	bind	9.11.12	cpe:2.3:a:isc:bind:9.11.12:s1:::supported_preview:::*
isc	bind	9.12.4	cpe:2.3:a:isc:bind:9.12.4:p1::::::
isc	bind	9.12.4	cpe:2.3:a:isc:bind:9.12.4:p2::::::
fedoraproject	fedora	30	cpe:2.3:o:fedoraproject:fedora:30:::::::*
fedoraproject	fedora	31	cpe:2.3:o:fedoraproject:fedora:31:::::::*

References for CVE-2019-6477

URL	Tags
http://lists.opensuse.org/opensuse-security-announce/2020-10/msg00041.html
http://lists.opensuse.org/opensuse-security-announce/2020-10/msg00044.html
https://kb.isc.org/docs/cve-2019-6477	Third Party Advisory
https://lists.fedoraproject.org/archives/list/package-announce%40lists.fedoraproject.org/message/L3DEMNZMKR57VQJCG5ZN55ZGTQRL2TFQ/
https://lists.fedoraproject.org/archives/list/package-announce%40lists.fedoraproject.org/message/XGURMGQHX45KR4QDRCSUQHODUFOGNGAN/
https://support.f5.com/csp/article/K15840535?utm_source=f5support&amp%3Butm_medium=RSS
https://www.debian.org/security/2020/dsa-4689
https://www.synology.com/security/advisory/Synology_SA_19_39	Third Party Advisory

URL

CVE-2019-6477 | TCP-pipelined queries can bypass tcp-clients limit

Exploit prediction scoring system (EPSS) score for CVE-2019-6477

Common vulnerability scoring system (CVSS) metrics for CVE-2019-6477

Weakness enumeration for CVE-2019-6477

OS Trackers for CVE-2019-6477

Affected software / configurations for CVE-2019-6477

References for CVE-2019-6477