CVE-2020-15240 [High] | Authentication Bypass in Omniauth-Auth0

omniauth-auth0 (rubygems) versions >= 2.3.0 and < 2.4.1 improperly validate the JWT token signature when using the `jwt_validator.verify` method. Improper validation of the JWT token signature can allow an attacker to bypass authentication and authorization. You are affected by this vulnerability if all of the following conditions apply: 1. You are using `omniauth-auth0`. 2. You are using `JWTValidator.verify` method directly OR you are not authenticating using the SDK’s default Authorization Code Flow. The issue is patched in version 2.4.1.

#	Date	Old EPSS score	New EPSS score	Delta (New - Old)
1	2026-06-15	0.15%	0.79%	+0.65%
2	2024-12-17	0.29%	0.15%	-0.15%
3	2024-08-25	—	0.29%	—

Date

Old EPSS score

New EPSS score

Delta (New - Old)

2026-06-15

0.15%

0.79%

+0.65%

2024-12-17

0.29%

0.15%

-0.15%

2024-08-25

—

0.29%

—

Base score	Version	Severity	Vector	Exploitability	Impact	Score source
7.4	3.1	HIGH	`CVSS:3.1/AV:N/AC:H/PR:N/UI:N/S:U/C:H/I:H/A:N` 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:H) Even with access, the exploit needs extra luck, timing, or a fussy environment to actually work. 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:H) Serious risk that confidential data gets exposed in a big way. Integrity (I:H) They could widely tamper with or forge data—trust in the data is badly hurt. Availability (A:N) Service keeps running; no real outage angle.	2.2	5.2	[email protected]
9.1	3.1	CRITICAL	`CVSS:3.1/AV:N/AC:L/PR:N/UI:N/S:U/C:H/I:H/A:N` 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:H) Serious risk that confidential data gets exposed in a big way. Integrity (I:H) They could widely tamper with or forge data—trust in the data is badly hurt. Availability (A:N) Service keeps running; no real outage angle.	3.9	5.2	[email protected]
5.8	2.0	MEDIUM	`AV:N/AC:M/Au:N/C:P/I:P/A:N` Click to expand Access vector (AV:N) Can be exploited remotely over network reachability. Access complexity (AC:M) Exploitation needs some favorable conditions, but not exceptional ones. Authentication (AU:N) No authentication is required. Confidentiality impact (C:P) Partial confidentiality impact. Integrity impact (I:P) Partial integrity impact. Availability impact (A:N) No availability impact.	8.6	4.9	[email protected]

Base score

Version

Severity

Vector

Exploitability

Impact

Score source

7.4

3.1

HIGH

CVSS:3.1/AV:N/AC:H/PR:N/UI:N/S:U/C:H/I:H/A:N 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:H): Even with access, the exploit needs extra luck, timing, or a fussy environment to actually work.
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:H): Serious risk that confidential data gets exposed in a big way.
Integrity (I:H): They could widely tamper with or forge data—trust in the data is badly hurt.
Availability (A:N): Service keeps running; no real outage angle.

2.2

5.2

[email protected]

9.1

3.1

CRITICAL

CVSS:3.1/AV:N/AC:L/PR:N/UI:N/S:U/C:H/I:H/A:N 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:H): Serious risk that confidential data gets exposed in a big way.
Integrity (I:H): They could widely tamper with or forge data—trust in the data is badly hurt.
Availability (A:N): Service keeps running; no real outage angle.

3.9

5.2

[email protected]

5.8

2.0

MEDIUM

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

Access vector (AV:N): Can be exploited remotely over network reachability.
Access complexity (AC:M): Exploitation needs some favorable conditions, but not exceptional ones.
Authentication (AU:N): No authentication is required.
Confidentiality impact (C:P): Partial confidentiality impact.
Integrity impact (I:P): Partial integrity impact.
Availability impact (A:N): No availability impact.

8.6

4.9

[email protected]

OS Trackers for CVE-2020-15240

vendor	priority	summary	link
`debian`	unimportant	CVE-2020-15240 unimportant priority: Debian including 1 source packages (ruby-omniauth-auth0), 1 status rows across 1 suites (bullseye): resolved 1.	https://security-tracker.debian.org/tracker/CVE-2020-15240
`ubuntu`	medium	CVE-2020-15240 medium priority: Ubuntu including 1 source packages (ruby-omniauth-auth0), 11 status rows across 11 suites (bionic, focal, groovy, hirsute, impish, jammy, kinetic, lunar, trusty, upstream, xenial): not-affected 8, DNE 3.	https://ubuntu.com/security/CVE-2020-15240

Affected software / configurations for CVE-2020-15240

Vendor	Product	Version	Raw CPE
auth0	omniauth-auth0	>= 2.3.0, < 2.4.1	cpe:2.3:a:auth0:omniauth-auth0::::::ruby::*

References for CVE-2020-15240

URL	Tags
https://github.com/auth0/omniauth-auth0/commit/fd3a14f4ccdfbc515d1121d6378ff88bf55a7a7a	Patch Third Party Advisory
https://github.com/auth0/omniauth-auth0/security/advisories/GHSA-58r4-h6v8-jcvm	Third Party Advisory
https://rubygems.org/gems/omniauth-auth0	Product Vendor Advisory

URL

CVE-2020-15240 | Regression in JWT Signature Validation

Exploit prediction scoring system (EPSS) score for CVE-2020-15240

Common vulnerability scoring system (CVSS) metrics for CVE-2020-15240

Weakness enumeration for CVE-2020-15240

GitHub Security Advisory for CVE-2020-15240

OS Trackers for CVE-2020-15240

Affected software / configurations for CVE-2020-15240

References for CVE-2020-15240