CVE-2020-28242 [Medium] | Security Vulnerability in Certified Asterisk

An issue was discovered in Asterisk Open Source 13.x before 13.37.1, 16.x before 16.14.1, 17.x before 17.8.1, and 18.x before 18.0.1 and Certified Asterisk before 16.8-cert5. If Asterisk is challenged on an outbound INVITE and the nonce is changed in each response, Asterisk will continually send INVITEs in a loop. This causes Asterisk to consume more and more memory since the transaction will never terminate (even if the call is hung up), ultimately leading to a restart or shutdown of Asterisk. Outbound authentication must be configured on the endpoint for this to occur.

#	Date	Old EPSS score	New EPSS score	Delta (New - Old)
1	2026-06-15	0.41%	1.54%	+1.13%
2	2026-01-16	0.59%	0.41%	-0.18%
3	2025-11-21	—	0.59%	—

Date

Old EPSS score

New EPSS score

Delta (New - Old)

2026-06-15

0.41%

1.54%

+1.13%

2026-01-16

0.59%

0.41%

-0.18%

2025-11-21

—

0.59%

—

Base score	Version	Severity	Vector	Exploitability	Impact	Score source
6.5	3.1	MEDIUM	`CVSS:3.1/AV:N/AC:L/PR:L/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:L) A normal user session is enough; they don’t have to be admin. 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.	2.8	3.6	[email protected]
4.0	2.0	MEDIUM	`AV:N/AC:L/Au:S/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:S) A single authentication is required. Confidentiality impact (C:N) No confidentiality impact. Integrity impact (I:N) No integrity impact. Availability impact (A:P) Partial availability impact.	8.0	2.9	[email protected]

Base score

Version

Severity

Vector

Exploitability

Impact

Score source

6.5

3.1

MEDIUM

CVSS:3.1/AV:N/AC:L/PR:L/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:L): A normal user session is enough; they don’t have to be admin.
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.

2.8

3.6

[email protected]

4.0

2.0

MEDIUM

AV:N/AC:L/Au:S/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:S): A single authentication is required.
Confidentiality impact (C:N): No confidentiality impact.
Integrity impact (I:N): No integrity impact.
Availability impact (A:P): Partial availability impact.

8.0

2.9

[email protected]

OS Trackers for CVE-2020-28242

vendor	priority	summary	link
`debian`	not yet assigned	CVE-2020-28242 not yet assigned priority: Debian including 1 source packages (asterisk), 2 status rows across 2 suites (bullseye, sid): resolved 2.	https://security-tracker.debian.org/tracker/CVE-2020-28242
`ubuntu`	medium	CVE-2020-28242 medium priority: Ubuntu including 1 source packages (asterisk), 16 status rows across 16 suites (bionic, focal, groovy, hirsute, impish, jammy, kinetic, lunar, mantic, noble, oracular, plucky, questing, trusty, upstream, xenial): not-affected 10, needed 3, DNE 1, ignored 1, released 1.	https://ubuntu.com/security/CVE-2020-28242

Affected software / configurations for CVE-2020-28242

Vendor	Product	Version	Raw CPE
asterisk	certified_asterisk	<= 16.8.0	cpe:2.3:a:asterisk:certified_asterisk::::::::
sangoma	asterisk	>= 13.0, < 13.37.1	cpe:2.3:a:sangoma:asterisk::::::::
sangoma	asterisk	>= 16.0, < 16.14.1	cpe:2.3:a:sangoma:asterisk::::::::
sangoma	asterisk	>= 17.0, < 17.8.1	cpe:2.3:a:sangoma:asterisk::::::::
sangoma	asterisk	>= 18.0, < 18.0.1	cpe:2.3:a:sangoma:asterisk::::::::
fedoraproject	fedora	33	cpe:2.3:o:fedoraproject:fedora:33:::::::*
debian	debian_linux	9.0	cpe:2.3:o:debian:debian_linux:9.0:::::::*

References for CVE-2020-28242

URL	Tags
http://downloads.asterisk.org/pub/security/AST-2020-002.html	Vendor Advisory
https://lists.debian.org/debian-lts-announce/2022/04/msg00001.html	Mailing List Third Party Advisory
https://lists.fedoraproject.org/archives/list/package-announce%40lists.fedoraproject.org/message/QUS54QTQCYKR36EIULYD544GXDA644HB/

URL

CVE-2020-28242

Exploit prediction scoring system (EPSS) score for CVE-2020-28242

Common vulnerability scoring system (CVSS) metrics for CVE-2020-28242

Weakness enumeration for CVE-2020-28242

OS Trackers for CVE-2020-28242

Affected software / configurations for CVE-2020-28242

References for CVE-2020-28242