CVE-2021-32777 [High] | Security Bypass in Envoy

Envoy is an open source L7 proxy and communication bus designed for large modern service oriented architectures. In affected versions when ext-authz extension is sending request headers to the external authorization service it must merge multiple value headers according to the HTTP spec. However, only the last header value is sent. This may allow specifically crafted requests to bypass authorization. Attackers may be able to escalate privileges when using ext-authz extension or back end service that uses multiple value headers for authorization. A specifically constructed request may be delivered by an untrusted downstream peer in the presence of ext-authz extension. Envoy versions 1.19.1, 1.18.4, 1.17.4, 1.16.5 contain fixes to the ext-authz extension to correctly merge multiple request header values, when sending request for authorization.

#	Date	Old EPSS score	New EPSS score	Delta (New - Old)
1	2025-03-17	0.09%	0.01%	-0.08%
2	2023-03-07	0.89%	0.09%	-0.80%
3	2022-04-01	—	0.89%	—

Date

Old EPSS score

New EPSS score

Delta (New - Old)

2025-03-17

0.09%

0.01%

-0.08%

2023-03-07

0.89%

0.09%

-0.80%

2022-04-01

—

0.89%

—

Base score	Version	Severity	Vector	Exploitability	Impact	Score source
8.6	3.1	HIGH	`CVSS:3.1/AV:N/AC:L/PR:N/UI:N/S:C/C:H/I:N/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:C) Breaking this can reach past the original component and bite other resources—bigger blast radius. Confidentiality (C:H) Serious risk that confidential data gets exposed in a big way. Integrity (I:N) Data isn’t meaningfully altered or forged. Availability (A:N) Service keeps running; no real outage angle.	3.9	4.0	[email protected]
8.3	3.1	HIGH	`CVSS:3.1/AV:N/AC:L/PR:N/UI:N/S:C/C:L/I:L/A:L` 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:C) Breaking this can reach past the original component and bite other resources—bigger blast radius. Confidentiality (C:L) Some sensitive info could get out, but not a total data dump. Integrity (I:L) Attackers could change some data, but it’s limited—not everything goes. Availability (A:L) Might cause slowdowns, glitches, or partial disruption—not a full brick.	3.9	3.7	[email protected]
7.5	2.0	HIGH	`AV:N/AC:L/Au:N/C:P/I:P/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:P) Partial confidentiality impact. Integrity impact (I:P) Partial integrity impact. Availability impact (A:P) Partial availability impact.	10.0	6.4	[email protected]

Base score

Version

Severity

Vector

Exploitability

Impact

Score source

8.6

3.1

HIGH

CVSS:3.1/AV:N/AC:L/PR:N/UI:N/S:C/C:H/I:N/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:C): Breaking this can reach past the original component and bite other resources—bigger blast radius.
Confidentiality (C:H): Serious risk that confidential data gets exposed in a big way.
Integrity (I:N): Data isn’t meaningfully altered or forged.
Availability (A:N): Service keeps running; no real outage angle.

3.9

4.0

[email protected]

8.3

3.1

HIGH

CVSS:3.1/AV:N/AC:L/PR:N/UI:N/S:C/C:L/I:L/A:L 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:C): Breaking this can reach past the original component and bite other resources—bigger blast radius.
Confidentiality (C:L): Some sensitive info could get out, but not a total data dump.
Integrity (I:L): Attackers could change some data, but it’s limited—not everything goes.
Availability (A:L): Might cause slowdowns, glitches, or partial disruption—not a full brick.

3.9

3.7

[email protected]

7.5

2.0

HIGH

AV:N/AC:L/Au:N/C:P/I:P/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:P): Partial confidentiality impact.
Integrity impact (I:P): Partial integrity impact.
Availability impact (A:P): Partial availability impact.

10.0

6.4

[email protected]

OS Trackers for CVE-2021-32777

vendor	priority	summary	link
`redhat`	high	—	https://access.redhat.com/security/cve/CVE-2021-32777

vendor

priority

summary

link

redhat

high

—

https://access.redhat.com/security/cve/CVE-2021-32777

Affected software / configurations for CVE-2021-32777

Vendor	Product	Version	Raw CPE
envoyproxy	envoy	>= 1.16.0, < 1.16.5	cpe:2.3:a:envoyproxy:envoy::::::::
envoyproxy	envoy	>= 1.17.0, < 1.17.4	cpe:2.3:a:envoyproxy:envoy::::::::
envoyproxy	envoy	>= 1.18.0, < 1.18.4	cpe:2.3:a:envoyproxy:envoy::::::::
envoyproxy	envoy	1.19.0	cpe:2.3:a:envoyproxy:envoy:1.19.0:::::::*

References for CVE-2021-32777

URL	Tags
https://github.com/envoyproxy/envoy/security/advisories/GHSA-6g4j-5vrw-2m8h	Third Party Advisory
https://www.envoyproxy.io/docs/envoy/v1.19.0/version_history/version_history	Release Notes Vendor Advisory

URL

CVE-2021-32777 | Incorrect concatenation of multiple value request headers in ext-authz extension

Exploit prediction scoring system (EPSS) score for CVE-2021-32777

Common vulnerability scoring system (CVSS) metrics for CVE-2021-32777

Weakness enumeration for CVE-2021-32777

OS Trackers for CVE-2021-32777

Affected software / configurations for CVE-2021-32777

References for CVE-2021-32777