# CVE-2021-32785: Format string bug in the Redis cache implementation

> A format string bug in mod_auth_openidc allows attackers to crash Apache workers via Redis cache interactions when encryption is disabled.

- **Severity:** Medium 5.3 (`CVSS:3.1/AV:N/AC:L/PR:N/UI:N/S:U/C:N/I:N/A:L`)
- **Exploited in the wild:** Not known
- **Login needed:** Not needed
- **Attackable:** Over the internet
- **Victim action needed:** Not needed
- **Fix available:** Yes
- **Published:** 22 Jul 2021
- **Updated:** 3 Aug 2024
- **Also known as:** AZL-6479, DEBIAN-CVE-2021-32785, GHSA-55r8-6w97-xxr4, UBUNTU-CVE-2021-32785

## What is CVE-2021-32785?

CVE-2021-32785 is a medium-severity vulnerability in Debian Debian Linux, published on 22 Jul 2021. An attacker can exploit it over the internet without logging in, with no action from the victim.

### Official description

mod_auth_openidc is an authentication/authorization module for the Apache 2.x HTTP server that functions as an OpenID Connect Relying Party, authenticating users against an OpenID Connect Provider. When mod_auth_openidc versions prior to 2.4.9 are configured to use an unencrypted Redis cache (`OIDCCacheEncrypt off`, `OIDCSessionType server-cache`, `OIDCCacheType redis`), `mod_auth_openidc` wrongly performed argument interpolation before passing Redis requests to `hiredis`, which would perform it again and lead to an uncontrolled format string bug. Initial assessment shows that this bug does not appear to allow gaining arbitrary code execution, but can reliably provoke a denial of service by repeatedly crashing the Apache workers. This bug has been corrected in version 2.4.9 by performing argument interpolation only once, using the `hiredis` API. As a workaround, this vulnerability can be mitigated by setting `OIDCCacheEncrypt` to `on`, as cache keys are cryptographically hashed before use when this option is enabled.

Weakness: CWE-134 (Use of Externally-Controlled Format String)

## Which versions are affected by CVE-2021-32785?

It affects 3 products.


Products: Debian Debian Linux, Netapp Cloud Backup, Openidc Mod Auth Openidc.

## How do I fix CVE-2021-32785?

Upgrade to a fixed version.

## Is CVE-2021-32785 being exploited?

There is no known exploitation of CVE-2021-32785 in the wild and no public exploit code.

## Other vulnerabilities in Debian Debian Linux

- [CVE-2015-3306](https://insights.sbomify.com/CVE-2015-3306/): ProFTPD Improper Access Control (critical 10.0, exploited in the wild)
- [CVE-2025-49113](https://insights.sbomify.com/CVE-2025-49113/): RoundCube Webmail Deserialization of Untrusted Data (critical 9.9, exploited in the wild)
- [CVE-2026-24061](https://insights.sbomify.com/CVE-2026-24061/): GNU InetUtils Argument Injection (critical 9.8, exploited in the wild)
- [CVE-2025-39682](https://insights.sbomify.com/CVE-2025-39682/): Linux Kernel Improper Check for Unusual or Exceptional Conditions (critical 9.8, exploited in the wild)
- [CVE-2024-9680](https://insights.sbomify.com/CVE-2024-9680/): Mozilla Firefox Use-After-Free (critical 9.8, exploited in the wild)

## Fix prompt for AI coding agents

```text
Check this codebase for CVE-2021-32785 and fix it if it is affected.

What it is: CVE-2021-32785 is a medium-severity vulnerability in Debian Debian Linux, published on 22 Jul 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-2021-32785 in the wild and no public exploit code.

Affected product: Debian Debian Linux. No package-level version data is available, so check the vendor advisory linked from the reference page.

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-2021-32785/ (Markdown: https://insights.sbomify.com/CVE-2021-32785/index.md)
```

## Sources

- CVE record: https://www.cve.org/CVERecord?id=CVE-2021-32785
- NVD: https://nvd.nist.gov/vuln/detail/CVE-2021-32785
- OSV: https://osv.dev/vulnerability/CVE-2021-32785

---
From sbomify Insights: https://insights.sbomify.com/CVE-2021-32785/
Summaries are generated and may contain mistakes; the official description above is the record.