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

> Attackers can bypass authorization checks in Envoy's ext-authz extension by crafting requests with multiple header values, potentially escalating privileges.

- **Severity:** High 8.6 (`CVSS:3.1/AV:N/AC:L/PR:N/UI:N/S:C/C:H/I:N/A:N`)
- **Exploited in the wild:** Not known
- **Login needed:** Not needed
- **Attackable:** Over the internet
- **Victim action needed:** Not needed
- **Fix available:** Yes
- **Published:** 24 Aug 2021
- **Updated:** 3 Aug 2024
- **Also known as:** BIT-envoy-2021-32777, GHSA-6g4j-5vrw-2m8h

## What is CVE-2021-32777?

CVE-2021-32777 is a high-severity authentication bypass vulnerability in Envoyproxy Envoy, published on 24 Aug 2021. An attacker can exploit it over the internet without logging in, with no action from the victim.

### Official 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.

Weakness: CWE-863 (Incorrect Authorization), CWE-551 (Incorrect Behavior Order: Authorization Before Parsing and Canonicalization)

## Which versions are affected by CVE-2021-32777?

1 open source package ship an affected version, including envoy. It affects 1 product.


| Package | Ecosystem | Affected | Fixed in |
| --- | --- | --- | --- |
| `envoy` | Bitnami | From 1.16.0 | 1.16.5, 1.17.4, 1.18.4, 1.19.1 |

Products: Envoyproxy Envoy.

## How do I fix CVE-2021-32777?

Upgrade envoy to a fixed version for your release line: 1.16.5, 1.17.4, 1.18.4 or 1.19.1.

## Is CVE-2021-32777 being exploited?

There is no known exploitation of CVE-2021-32777 in the wild and no public exploit code.

## Other vulnerabilities in Envoyproxy Envoy

- [CVE-2022-29226](https://insights.sbomify.com/CVE-2022-29226/): Trivial authentication bypass in Envoy (critical 10.0)
- [CVE-2019-18801](https://insights.sbomify.com/CVE-2019-18801/): Memory corruption in n/a (critical 9.8)
- [CVE-2019-18802](https://insights.sbomify.com/CVE-2019-18802/): Security feature bypass in n/a (critical 9.8)
- [CVE-2020-35470](https://insights.sbomify.com/CVE-2020-35470/): Information disclosure in n/a (high 8.8)
- [CVE-2024-23324](https://insights.sbomify.com/CVE-2024-23324/): Envoy ext auth can be bypassed when Proxy protocol filter sets invalid UTF-8 metadata (high 8.6)

## Fix prompt for AI coding agents

```text
Check this codebase for CVE-2021-32777 and fix it if it is affected.

What it is: CVE-2021-32777 is a high-severity authentication bypass vulnerability in Envoyproxy Envoy, published on 24 Aug 2021. An attacker can exploit it over the internet without logging in, with no action from the victim.
Exploitation: There is no known exploitation of CVE-2021-32777 in the wild and no public exploit code.

Affected packages and fixed versions:
- envoy (Bitnami): affected from 1.16.0; fixed in 1.16.5, 1.17.4, 1.18.4, 1.19.1

Task:
1. Search the dependency manifests and lockfiles (for example package.json, package-lock.json, requirements.txt, poetry.lock, uv.lock, pom.xml, build.gradle, go.mod, Cargo.lock, Gemfile.lock) and any Dockerfiles for the affected packages, including transitive dependencies.
2. If an affected version is in use, upgrade it to the fixed version for its release line with the project's package manager, so the lockfile is regenerated. Prefer the smallest upgrade that fixes it.
3. If there is no fix, or the upgrade would break the build, do not guess: explain the risk and the safest workaround instead.
4. Run the tests and summarise what changed and why.
5. If nothing in the project is affected, say so and change nothing.

Reference: https://insights.sbomify.com/CVE-2021-32777/ (Markdown: https://insights.sbomify.com/CVE-2021-32777/index.md)
```

## Sources

- CVE record: https://www.cve.org/CVERecord?id=CVE-2021-32777
- NVD: https://nvd.nist.gov/vuln/detail/CVE-2021-32777
- OSV: https://osv.dev/vulnerability/CVE-2021-32777

---
From sbomify Insights: https://insights.sbomify.com/CVE-2021-32777/
Summaries are generated and may contain mistakes; the official description above is the record.