# CVE-2021-32781: Continued processing of requests after locally generated response

> Attackers can cause a denial of service in Envoy proxy by triggering a use-after-free condition when specific extensions modify request or response bodies.

- **Severity:** High 8.6 (`CVSS:3.1/AV:N/AC:L/PR:N/UI:N/S:C/C:N/I:N/A:H`)
- **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-2021-32781, GHSA-5vhv-gp9v-42qv

## What is CVE-2021-32781?

CVE-2021-32781 is a high-severity use after free 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 after Envoy sends a locally generated response it must stop further processing of request or response data. However when local response is generated due the internal buffer overflow while request or response is processed by the filter chain the operation may not be stopped completely and result in accessing a freed memory block. A specifically constructed request delivered by an untrusted downstream or upstream peer in the presence of extensions that modify and increase the size of request or response bodies resulting in a Denial of Service when using extensions that modify and increase the size of request or response bodies, such as decompressor filter. Envoy versions 1.19.1, 1.18.4, 1.17.4, 1.16.5 contain fixes to address incomplete termination of request processing after locally generated response. As a workaround disable Envoy's decompressor, json-transcoder or grpc-web extensions or proprietary extensions that modify and increase the size of request or response bodies, if feasible.

Weakness: CWE-120 (Buffer Copy without Checking Size of Input), CWE-416 (Use After Free)

## Which versions are affected by CVE-2021-32781?

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-2021-32781?

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-2021-32781 being exploited?

There is no known exploitation of CVE-2021-32781 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-2021-32781 and fix it if it is affected.

What it is: CVE-2021-32781 is a high-severity use after free 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-2021-32781 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-2021-32781/ (Markdown: https://insights.sbomify.com/CVE-2021-32781/index.md)
```

## Sources

- CVE record: https://www.cve.org/CVERecord?id=CVE-2021-32781
- NVD: https://nvd.nist.gov/vuln/detail/CVE-2021-32781
- OSV: https://osv.dev/vulnerability/CVE-2021-32781

---
From sbomify Insights: https://insights.sbomify.com/CVE-2021-32781/
Summaries are generated and may contain mistakes; the official description above is the record.