# CVE-2023-27535: Auth bypass in https://github.com/curl/curl

> An authentication bypass in libcurl's FTP connection reuse allows attackers to use wrong credentials, potentially accessing sensitive information.

- **Severity:** Medium 5.9 (`CVSS:3.1/AV:N/AC:H/PR:N/UI:N/S:U/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:** 30 Mar 2023
- **Updated:** 14 Oct 2026
- **Also known as:** ALPINE-CVE-2023-27535, ALSA-2023:2650, ALSA-2023:3106, AZL-25787, AZL-25805, AZL-25811, AZL-25846, AZL-34611, AZL-38512, CLEANSTART-2026-LQ81593, CURL-CVE-2023-27535, DEBIAN-CVE-2023-27535, GHSA-q9fm-68jc-87x3, JLSEC-2025-31, RHSA-2023:2650, RHSA-2023:3106, RLSA-2023:3106, UBUNTU-CVE-2023-27535

## What is CVE-2023-27535?

CVE-2023-27535 is a medium-severity authentication bypass vulnerability in Debian Debian Linux, published on 30 Mar 2023. An attacker can exploit it over the internet without logging in, with no action from the victim.

### Official description

An authentication bypass vulnerability exists in libcurl <8.0.0 in the FTP connection reuse feature that can result in wrong credentials being used during subsequent transfers. Previously created connections are kept in a connection pool for reuse if they match the current setup. However, certain FTP settings such as CURLOPT_FTP_ACCOUNT, CURLOPT_FTP_ALTERNATIVE_TO_USER, CURLOPT_FTP_SSL_CCC, and CURLOPT_USE_SSL were not included in the configuration match checks, causing them to match too easily. This could lead to libcurl using the wrong credentials when performing a transfer, potentially allowing unauthorized access to sensitive information.

Weakness: CWE-287 (Improper Authentication), CWE-305 (Authentication Bypass by Primary Weakness)

## Which versions are affected by CVE-2023-27535?

It affects 10 products.


| Package | Ecosystem | Affected | Fixed in |
| --- | --- | --- | --- |
| `curl` | AlmaLinux:8 | All versions | 7.61.1-30.el8_8.2 |
| `libcurl` | AlmaLinux:8 | All versions | 7.61.1-30.el8_8.2 |
| `libcurl-devel` | AlmaLinux:8 | All versions | 7.61.1-30.el8_8.2 |
| `libcurl-minimal` | AlmaLinux:8 | All versions | 7.61.1-30.el8_8.2 |
| `curl` | AlmaLinux:9 | All versions | 7.76.1-23.el9_2.1 |
| `curl-minimal` | AlmaLinux:9 | All versions | 7.76.1-23.el9_2.1 |
| `libcurl` | AlmaLinux:9 | All versions | 7.76.1-23.el9_2.1 |
| `libcurl-devel` | AlmaLinux:9 | All versions | 7.76.1-23.el9_2.1 |
| `libcurl-minimal` | AlmaLinux:9 | All versions | 7.76.1-23.el9_2.1 |
| `curl` | Red Hat:enterprise_linux:8::baseos | All versions | 0:7.61.1-30.el8_8.2 |
| `curl-debuginfo` | Red Hat:enterprise_linux:8::baseos | All versions | 0:7.61.1-30.el8_8.2 |
| `curl-debugsource` | Red Hat:enterprise_linux:8::baseos | All versions | 0:7.61.1-30.el8_8.2 |
| `curl-minimal-debuginfo` | Red Hat:enterprise_linux:8::baseos | All versions | 0:7.61.1-30.el8_8.2 |
| `libcurl` | Red Hat:enterprise_linux:8::baseos | All versions | 0:7.61.1-30.el8_8.2 |
| `libcurl-debuginfo` | Red Hat:enterprise_linux:8::baseos | All versions | 0:7.61.1-30.el8_8.2 |
| `libcurl-devel` | Red Hat:enterprise_linux:8::baseos | All versions | 0:7.61.1-30.el8_8.2 |
| `libcurl-minimal` | Red Hat:enterprise_linux:8::baseos | All versions | 0:7.61.1-30.el8_8.2 |
| `libcurl-minimal-debuginfo` | Red Hat:enterprise_linux:8::baseos | All versions | 0:7.61.1-30.el8_8.2 |
| `curl-debuginfo` | Red Hat:enterprise_linux:9::appstream | All versions | 0:7.76.1-23.el9_2.1 |
| `curl-debugsource` | Red Hat:enterprise_linux:9::appstream | All versions | 0:7.76.1-23.el9_2.1 |
| `curl-minimal-debuginfo` | Red Hat:enterprise_linux:9::appstream | All versions | 0:7.76.1-23.el9_2.1 |
| `libcurl-debuginfo` | Red Hat:enterprise_linux:9::appstream | All versions | 0:7.76.1-23.el9_2.1 |
| `libcurl-devel` | Red Hat:enterprise_linux:9::appstream | All versions | 0:7.76.1-23.el9_2.1 |
| `libcurl-minimal-debuginfo` | Red Hat:enterprise_linux:9::appstream | All versions | 0:7.76.1-23.el9_2.1 |
| `curl` | Red Hat:enterprise_linux:9::baseos | All versions | 0:7.76.1-23.el9_2.1 |
| `curl-debuginfo` | Red Hat:enterprise_linux:9::baseos | All versions | 0:7.76.1-23.el9_2.1 |
| `curl-debugsource` | Red Hat:enterprise_linux:9::baseos | All versions | 0:7.76.1-23.el9_2.1 |
| `curl-minimal` | Red Hat:enterprise_linux:9::baseos | All versions | 0:7.76.1-23.el9_2.1 |
| `curl-minimal-debuginfo` | Red Hat:enterprise_linux:9::baseos | All versions | 0:7.76.1-23.el9_2.1 |
| `libcurl` | Red Hat:enterprise_linux:9::baseos | All versions | 0:7.76.1-23.el9_2.1 |
| `libcurl-debuginfo` | Red Hat:enterprise_linux:9::baseos | All versions | 0:7.76.1-23.el9_2.1 |
| `libcurl-minimal` | Red Hat:enterprise_linux:9::baseos | All versions | 0:7.76.1-23.el9_2.1 |
| `libcurl-minimal-debuginfo` | Red Hat:enterprise_linux:9::baseos | All versions | 0:7.76.1-23.el9_2.1 |
| `curl` | Rocky Linux:8 | All versions | 0:7.61.1-30.el8_8.2 |

Products: Debian Debian Linux, Fedoraproject Fedora, Haxx Libcurl, Netapp Active Iq Unified Manager, Netapp H300s Firmware, Netapp H410s Firmware, Netapp H500s Firmware, Netapp H700s Firmware, Netapp Ontap 9, Splunk Universal Forwarder.

## How do I fix CVE-2023-27535?

Upgrade to a fixed version.

## Is CVE-2023-27535 being exploited?

It is not confirmed as exploited in the wild, but public exploit code for CVE-2023-27535 exists.

## 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-2023-27535 and fix it if it is affected.

What it is: CVE-2023-27535 is a medium-severity authentication bypass vulnerability in Debian Debian Linux, published on 30 Mar 2023. An attacker can exploit it over the internet without logging in, with no action from the victim.
Exploitation: It is not confirmed as exploited in the wild, but public exploit code for CVE-2023-27535 exists.

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-2023-27535/ (Markdown: https://insights.sbomify.com/CVE-2023-27535/index.md)
```

## Sources

- CVE record: https://www.cve.org/CVERecord?id=CVE-2023-27535
- NVD: https://nvd.nist.gov/vuln/detail/CVE-2023-27535
- OSV: https://osv.dev/vulnerability/CVE-2023-27535

---
From sbomify Insights: https://insights.sbomify.com/CVE-2023-27535/
Summaries are generated and may contain mistakes; the official description above is the record.