# CVE-2021-3618: Other in ALPACA > Man-in-the-middle attackers can redirect traffic between subdomains sharing certificates, breaking TLS authentication and enabling cross-protocol attacks. - **Severity:** High 7.4 (`CVSS:3.1/AV:N/AC:H/PR:N/UI:N/S:U/C:H/I:H/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:** 23 Mar 2022 - **Updated:** 3 Aug 2024 - **Also known as:** ALPINE-CVE-2021-3618, AZL-9188, AZL-9190, AZL-9220, BIT-nginx-2021-3618, BIT-nginx-gateway-2021-3618, CLEANSTART-2026-IT95169, CLSA-2022-1649695619, CLSA-2022-1649695737, CLSA-2022-1649695783, CLSA-2022-1649696332, CLSA-2022-1649696379, DEBIAN-CVE-2021-3618, GHSA-r9r5-jxp7-whr4, MGASA-2021-0540, OESA-2022-1637, SUSE-RU-2022:0655-1, SUSE-SU-2022:3320-1, SUSE-SU-2022:3383-1, SUSE-SU-2022:3457-1, SUSE-SU-2022:3458-1, SUSE-SU-2022:3888-1, SUSE-SU-2022:4192-1, SUSE-SU-2022:4201-1, SUSE-SU-2022:4265-1, SUSE-SU-2022:4266-1, UBUNTU-CVE-2021-3618, USN-5371-2, USN-6379-1 ## What is CVE-2021-3618? CVE-2021-3618 is a high-severity vulnerability in Debian Debian Linux, published on 23 Mar 2022. An attacker can exploit it over the internet without logging in, with no action from the victim. ### Official description ALPACA is an application layer protocol content confusion attack, exploiting TLS servers implementing different protocols but using compatible certificates, such as multi-domain or wildcard certificates. A MiTM attacker having access to victim's traffic at the TCP/IP layer can redirect traffic from one subdomain to another, resulting in a valid TLS session. This breaks the authentication of TLS and cross-protocol attacks may be possible where the behavior of one protocol service may compromise the other at the application layer. Weakness: CWE-295 (Improper Certificate Validation) ## Which versions are affected by CVE-2021-3618? 2 open source packages ship an affected version, including nginx and nginx-gateway. It affects 5 products. | Package | Ecosystem | Affected | Fixed in | | --- | --- | --- | --- | | `nginx` | Bitnami | All versions | 1.21.0 | | `nginx-gateway` | Bitnami | All versions | 1.21.0 | | `nginx` | SUSE:Enterprise Storage 6 | All versions | 1.16.1-150100.6.16.1 | | `vsftpd` | SUSE:Enterprise Storage 6 | All versions | 3.0.5-150000.7.19.1 | | `nginx` | SUSE:Enterprise Storage 7 | All versions | 1.16.1-150200.3.9.1 | | `vsftpd` | SUSE:Enterprise Storage 7 | All versions | 3.0.5-150200.12.9.1 | | `nginx` | SUSE:Linux Enterprise High Performance Computing 15 SP1-ESPOS | All versions | 1.16.1-150100.6.16.1 | | `vsftpd` | SUSE:Linux Enterprise High Performance Computing 15 SP1-ESPOS | All versions | 3.0.5-150000.7.19.1 | | `nginx` | SUSE:Linux Enterprise High Performance Computing 15 SP1-LTSS | All versions | 1.16.1-150100.6.16.1 | | `vsftpd` | SUSE:Linux Enterprise High Performance Computing 15 SP1-LTSS | All versions | 3.0.5-150000.7.19.1 | | `nginx` | SUSE:Linux Enterprise High Performance Computing 15 SP2-ESPOS | All versions | 1.16.1-150200.3.9.1 | | `vsftpd` | SUSE:Linux Enterprise High Performance Computing 15 SP2-ESPOS | All versions | 3.0.5-150200.12.9.1 | | `nginx` | SUSE:Linux Enterprise High Performance Computing 15 SP2-LTSS | All versions | 1.16.1-150200.3.9.1 | | `vsftpd` | SUSE:Linux Enterprise High Performance Computing 15 SP2-LTSS | All versions | 3.0.5-150200.12.9.1 | | `nginx` | SUSE:Linux Enterprise High Performance Computing 15-ESPOS | All versions | 1.16.1-150000.3.18.1 | | `vsftpd` | SUSE:Linux Enterprise High Performance Computing 15-ESPOS | All versions | 3.0.5-150000.7.19.1 | | `nginx` | SUSE:Linux Enterprise High Performance Computing 15-LTSS | All versions | 1.16.1-150000.3.18.1 | | `vsftpd` | SUSE:Linux Enterprise High Performance Computing 15-LTSS | All versions | 3.0.5-150000.7.19.1 | | `nginx` | SUSE:Linux Enterprise Module for Server Applications 15 SP3 | All versions | 1.19.8-150300.3.9.1 | | `vsftpd` | SUSE:Linux Enterprise Module for Server Applications 15 SP3 | All versions | 3.0.5-150200.12.9.1 | | `vsftpd` | SUSE:Linux Enterprise Module for Server Applications 15 SP4 | All versions | 3.0.5-150400.3.3.1 | | `vsftpd` | SUSE:Linux Enterprise Server 12 SP5 | All versions | 3.0.5-47.7.1 | | `vsftpd` | SUSE:Linux Enterprise Server 12 SP5 | All versions | 3.0.5-48.3.1 | | `vsftpd` | SUSE:Linux Enterprise Server 12 SP5 | All versions | 3.0.5-51.1 | | `nginx` | SUSE:Linux Enterprise Server 15 SP1-BCL | All versions | 1.16.1-150100.6.16.1 | | `vsftpd` | SUSE:Linux Enterprise Server 15 SP1-BCL | All versions | 3.0.5-150000.7.19.1 | | `nginx` | SUSE:Linux Enterprise Server 15 SP1-LTSS | All versions | 1.16.1-150100.6.16.1 | | `vsftpd` | SUSE:Linux Enterprise Server 15 SP1-LTSS | All versions | 3.0.5-150000.7.19.1 | | `nginx` | SUSE:Linux Enterprise Server 15 SP2-BCL | All versions | 1.16.1-150200.3.9.1 | | `vsftpd` | SUSE:Linux Enterprise Server 15 SP2-BCL | All versions | 3.0.5-150200.12.9.1 | | `nginx` | SUSE:Linux Enterprise Server 15 SP2-LTSS | All versions | 1.16.1-150200.3.9.1 | | `vsftpd` | SUSE:Linux Enterprise Server 15 SP2-LTSS | All versions | 3.0.5-150200.12.9.1 | | `nginx` | SUSE:Linux Enterprise Server 15-LTSS | All versions | 1.16.1-150000.3.18.1 | | `vsftpd` | SUSE:Linux Enterprise Server 15-LTSS | All versions | 3.0.5-150000.7.19.1 | | `vsftpd` | SUSE:Linux Enterprise Server for SAP Applications 12 SP5 | All versions | 3.0.5-47.7.1 | | `vsftpd` | SUSE:Linux Enterprise Server for SAP Applications 12 SP5 | All versions | 3.0.5-48.3.1 | | `vsftpd` | SUSE:Linux Enterprise Server for SAP Applications 12 SP5 | All versions | 3.0.5-51.1 | | `nginx` | SUSE:Linux Enterprise Server for SAP Applications 15 | All versions | 1.16.1-150000.3.18.1 | | `vsftpd` | SUSE:Linux Enterprise Server for SAP Applications 15 | All versions | 3.0.5-150000.7.19.1 | | `nginx` | SUSE:Linux Enterprise Server for SAP Applications 15 SP1 | All versions | 1.16.1-150100.6.16.1 | Products: Debian Debian Linux, F5 Nginx, Fedoraproject Fedora, Sendmail Sendmail, Vsftpd Project Vsftpd. ## How do I fix CVE-2021-3618? Upgrade nginx to 1.21.0 or later. ## Is CVE-2021-3618 being exploited? There is no known exploitation of CVE-2021-3618 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-2021-3618 and fix it if it is affected. What it is: CVE-2021-3618 is a high-severity vulnerability in Debian Debian Linux, published on 23 Mar 2022. 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-2021-3618 in the wild and no public exploit code. Affected packages and fixed versions: - nginx (Bitnami): affected all versions; fixed in 1.21.0 - nginx-gateway (Bitnami): affected all versions; fixed in 1.21.0 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-2021-3618/ (Markdown: https://insights.sbomify.com/CVE-2021-3618/index.md) ``` ## Sources - CVE record: https://www.cve.org/CVERecord?id=CVE-2021-3618 - NVD: https://nvd.nist.gov/vuln/detail/CVE-2021-3618 - OSV: https://osv.dev/vulnerability/CVE-2021-3618 --- From sbomify Insights: https://insights.sbomify.com/CVE-2021-3618/ Summaries are generated and may contain mistakes; the official description above is the record.