# CVE-2021-21603: XSS vulnerability in Jenkins notification bar

> An attacker can inject malicious scripts into Jenkins notification bars, potentially leading to session hijacking or code execution.

- **Severity:** Medium 5.4 (`CVSS:3.1/AV:N/AC:L/PR:L/UI:R/S:C/C:L/I:L/A:N`)
- **Exploited in the wild:** Not known
- **Login needed:** Any signed-in user
- **Attackable:** Over the internet
- **Victim action needed:** A user has to click or open something
- **Fix available:** Yes
- **Published:** 13 Jan 2021
- **Updated:** 3 Aug 2024
- **Also known as:** BIT-jenkins-2021-21603, GHSA-98gq-6hxg-52r6

## What is CVE-2021-21603?

CVE-2021-21603 is a medium-severity cross-site scripting vulnerability in Jenkins Jenkins, published on 13 Jan 2021. Any signed-in user can exploit it over the network, and only if a user opens a file or follows a link.

### Official description

Jenkins 2.274 and earlier, LTS 2.263.1 and earlier does not escape notification bar response contents, resulting in a cross-site scripting (XSS) vulnerability.

Weakness: CWE-79 (Improper Neutralization of Input During Web Page Generation)

## Which versions are affected by CVE-2021-21603?

5 open source packages ship an affected version, including org.jenkins-ci.main:jenkins-core and jenkins. It affects 1 product.


| Package | Ecosystem | Affected | Fixed in |
| --- | --- | --- | --- |
| `org.jenkins-ci.main:jenkins-core` | Maven | All versions | 2.275 |
| `org.jenkins-ci.main:jenkins-core` | Maven | All versions | 2.275 |
| `org.jenkins-ci.main:jenkins-core` | Maven | From 2.263.2 | 2.275 |
| `org.jenkins-ci.main:jenkins-core` | Maven | From 2.263.2 | 2.275 |
| `jenkins` | Bitnami | All versions | 2.274.1 |

Products: Jenkins Jenkins.

## How do I fix CVE-2021-21603?

Upgrade org.jenkins-ci.main:jenkins-core to 2.275 or later.

## Is CVE-2021-21603 being exploited?

There is no known exploitation of CVE-2021-21603 in the wild and no public exploit code.

## Other vulnerabilities in Jenkins Jenkins

- [CVE-2024-23897](https://insights.sbomify.com/CVE-2024-23897/): Jenkins Command Line Interface (CLI) Path Traversal (critical 9.8, exploited in the wild)
- [CVE-2018-1000861](https://insights.sbomify.com/CVE-2018-1000861/): Jenkins Stapler Web Framework Deserialization of Untrusted Data (critical 9.8, exploited in the wild)
- [CVE-2017-1000353](https://insights.sbomify.com/CVE-2017-1000353/): Jenkins Remote Code Execution (critical 9.8, exploited in the wild)
- [CVE-2015-5317](https://insights.sbomify.com/CVE-2015-5317/): Jenkins User Interface (UI) Information Disclosure (high 7.5, exploited in the wild)
- [CVE-2021-21690](https://insights.sbomify.com/CVE-2021-21690/): Multiple vulnerabilities allow bypassing path filtering of agent-to-controller access control in Jenkins (critical 9.8)

## Fix prompt for AI coding agents

```text
Check this codebase for CVE-2021-21603 and fix it if it is affected.

What it is: CVE-2021-21603 is a medium-severity cross-site scripting vulnerability in Jenkins Jenkins, published on 13 Jan 2021. Any signed-in user can exploit it over the network, and only if a user opens a file or follows a link.
Exploitation: There is no known exploitation of CVE-2021-21603 in the wild and no public exploit code.

Affected packages and fixed versions:
- org.jenkins-ci.main:jenkins-core (Maven): affected all versions; fixed in 2.275
- org.jenkins-ci.main:jenkins-core (Maven): affected all versions; fixed in 2.275
- org.jenkins-ci.main:jenkins-core (Maven): affected from 2.263.2; fixed in 2.275
- org.jenkins-ci.main:jenkins-core (Maven): affected from 2.263.2; fixed in 2.275
- jenkins (Bitnami): affected all versions; fixed in 2.274.1

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-2021-21603/ (Markdown: https://insights.sbomify.com/CVE-2021-21603/index.md)
```

## Sources

- CVE record: https://www.cve.org/CVERecord?id=CVE-2021-21603
- NVD: https://nvd.nist.gov/vuln/detail/CVE-2021-21603
- OSV: https://osv.dev/vulnerability/CVE-2021-21603

---
From sbomify Insights: https://insights.sbomify.com/CVE-2021-21603/
Summaries are generated and may contain mistakes; the official description above is the record.