SOC status:Duty analyst on shift

UK Cyber Defence
VulnerabilityModified

CVE-2021-32777

This may allow specifically crafted requests to bypass authorization.

HIGH 8.3EPSS 3.33%

Does this matter?

High impact if exploited, but EPSS currently rates exploitation as unlikely (3.33%). Schedule it in the normal patch cycle and watch for a rise in EPSS or a public exploit.

Description

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.

CVSS 3.1
8.3 HIGHCVSS:3.1/AV:N/AC:L/PR:N/UI:N/S:C/C:L/I:L/A:L
EPSS
3.33% probability · 89th percentile
Public exploits
None in Exploit-DB
CISA KEV
Not listed
Weakness
CWE-551, CWE-863
Affected
envoyproxy/envoy
Source
security-advisories@github.com
EPSS trend
0%3%5%26 October 2026: 3.33%26 October 202626 October 2026

EPSS 3.3% since 26 October 2026; no change recorded yet. Points are recorded when the score first appears and whenever it moves by a percentage point or more.

References

Source: NVD record, EPSS from FIRST.org, KEV from CISA, exploits from Exploit-DB. Refreshed daily. Download this record as JSON.