# CVE-2016-8616: Auth bypass in curl

> Attackers can bypass authentication by exploiting case-insensitive credential checks to reuse existing connections with valid credentials.

- **Severity:** Low 3.7 (`CVSS:3.0/AV:N/AC:H/PR:N/UI:N/S:U/C:N/I:L/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:** 1 Aug 2018
- **Updated:** 6 Aug 2024
- **Also known as:** ALPINE-CVE-2016-8616, CLEANSTART-2026-KR73737, CURL-CVE-2016-8616, DEBIAN-CVE-2016-8616, GHSA-22qv-x7vv-h86h, UBUNTU-CVE-2016-8616

## What is CVE-2016-8616?

CVE-2016-8616 is a low-severity authentication bypass vulnerability in Haxx Curl, published on 1 Aug 2018. An attacker can exploit it over the internet without logging in, with no action from the victim.

### Official description

A flaw was found in curl before version 7.51.0 When re-using a connection, curl was doing case insensitive comparisons of user name and password with the existing connections. This means that if an unused connection with proper credentials exists for a protocol that has connection-scoped credentials, an attacker can cause that connection to be reused if s/he knows the case-insensitive version of the correct password.

Weakness: CWE-255, CWE-592 (DEPRECATED: Authentication Bypass Issues)

## Which versions are affected by CVE-2016-8616?

It affects 1 product.


Products: Haxx Curl.

## How do I fix CVE-2016-8616?

Upgrade to a fixed version.

## Is CVE-2016-8616 being exploited?

There is no known exploitation of CVE-2016-8616 in the wild and no public exploit code.

## Other vulnerabilities in Haxx Curl

- [CVE-2026-19931](https://insights.sbomify.com/CVE-2026-19931/): Negotiate ambient user conn reuse (critical 9.8)
- [CVE-2026-10536](https://insights.sbomify.com/CVE-2026-10536/): HTTP/2 stream-dependency tree UAF (critical 9.8)
- [CVE-2026-11856](https://insights.sbomify.com/CVE-2026-11856/): cross-origin Digest auth state leak (critical 9.8)
- [CVE-2026-8925](https://insights.sbomify.com/CVE-2026-8925/): SASL double-free (critical 9.8)
- [CVE-2026-9079](https://insights.sbomify.com/CVE-2026-9079/): stale proxy password leak (critical 9.8)

## Fix prompt for AI coding agents

```text
Check this codebase for CVE-2016-8616 and fix it if it is affected.

What it is: CVE-2016-8616 is a low-severity authentication bypass vulnerability in Haxx Curl, published on 1 Aug 2018. 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-2016-8616 in the wild and no public exploit code.

Affected product: Haxx Curl. 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-2016-8616/ (Markdown: https://insights.sbomify.com/CVE-2016-8616/index.md)
```

## Sources

- CVE record: https://www.cve.org/CVERecord?id=CVE-2016-8616
- NVD: https://nvd.nist.gov/vuln/detail/CVE-2016-8616
- OSV: https://osv.dev/vulnerability/CVE-2016-8616

---
From sbomify Insights: https://insights.sbomify.com/CVE-2016-8616/
Summaries are generated and may contain mistakes; the official description above is the record.