# CVE-2020-26258: Server-Side Forgery Request can be activated unmarshalling with XStream > Remote attackers can trigger Server-Side Request Forgery in XStream when unmarshalling XML if using the default blacklist configuration. - **Severity:** Medium 6.3 (`CVSS:3.1/AV:N/AC:H/PR:L/UI:N/S:C/C:H/I:N/A:N`) - **Exploited in the wild:** Not known - **Login needed:** Any signed-in user - **Attackable:** Over the internet - **Victim action needed:** Not needed - **Fix available:** Yes - **Published:** 16 Dec 2020 - **Updated:** 7 Oct 2026 - **Also known as:** DEBIAN-CVE-2020-26258, GHSA-4cch-wxpw-8p28, UBUNTU-CVE-2020-26258 ## What is CVE-2020-26258? CVE-2020-26258 is a medium-severity server-side request forgery vulnerability in Apache Struts, published on 16 Dec 2020. Any signed-in user can exploit it over the network, with no action from the victim. ### Official description XStream is a Java library to serialize objects to XML and back again. In XStream before version 1.4.15, a Server-Side Forgery Request vulnerability can be activated when unmarshalling. The vulnerability may allow a remote attacker to request data from internal resources that are not publicly available only by manipulating the processed input stream. If you rely on XStream's default blacklist of the Security Framework, you will have to use at least version 1.4.15. The reported vulnerability does not exist if running Java 15 or higher. No user is affected who followed the recommendation to setup XStream's Security Framework with a whitelist! Anyone relying on XStream's default blacklist can immediately switch to a whilelist for the allowed types to avoid the vulnerability. Users of XStream 1.4.14 or below who still want to use XStream default blacklist can use a workaround described in more detailed in the referenced advisories. Weakness: CWE-918 (Server-Side Request Forgery) ## Which versions are affected by CVE-2020-26258? 2 open source packages ship an affected version, including com.thoughtworks.xstream:xstream. It affects 4 products. | Package | Ecosystem | Affected | Fixed in | | --- | --- | --- | --- | | `com.thoughtworks.xstream:xstream` | Maven | All versions | 1.4.15 | | `com.thoughtworks.xstream:xstream` | Maven | All versions | 1.4.15 | Products: Apache Struts, Debian Debian Linux, Fedoraproject Fedora, Xstream Xstream. ## How do I fix CVE-2020-26258? Upgrade com.thoughtworks.xstream:xstream to 1.4.15 or later. ## Is CVE-2020-26258 being exploited? It is not confirmed as exploited in the wild, but public exploit code for CVE-2020-26258 exists. Public exploit code: - CVE-2020-26258 && XStream SSRF (github_poc): https://github.com/Al1ex/CVE-2020-26258 - https://github.com/cuijiung/xstream-CVE-2020-26258 (github_poc): https://github.com/cuijiung/xstream-CVE-2020-26258 - XStream <1.4.15 - Server-Side Request Forgery (nuclei): http/cves/2020/CVE-2020-26258.yaml ## Other vulnerabilities in Apache Struts - [CVE-2020-17530](https://insights.sbomify.com/CVE-2020-17530/): Apache Struts Remote Code Execution (critical 9.8, exploited in the wild) - [CVE-2017-9791](https://insights.sbomify.com/CVE-2017-9791/): Apache Struts 1 Improper Input Validation (critical 9.8, exploited in the wild) - [CVE-2017-5638](https://insights.sbomify.com/CVE-2017-5638/): Apache Struts Remote Code Execution (critical 9.8, exploited in the wild) - [CVE-2012-0391](https://insights.sbomify.com/CVE-2012-0391/): Apache Struts 2 Improper Input Validation (critical 9.8, exploited in the wild) - [CVE-2018-11776](https://insights.sbomify.com/CVE-2018-11776/): Apache Struts Remote Code Execution (high 8.1, exploited in the wild) ## Fix prompt for AI coding agents ```text Check this codebase for CVE-2020-26258 and fix it if it is affected. What it is: CVE-2020-26258 is a medium-severity server-side request forgery vulnerability in Apache Struts, published on 16 Dec 2020. Any signed-in user can exploit it over the network, with no action from the victim. Exploitation: It is not confirmed as exploited in the wild, but public exploit code for CVE-2020-26258 exists. Affected packages and fixed versions: - com.thoughtworks.xstream:xstream (Maven): affected all versions; fixed in 1.4.15 - com.thoughtworks.xstream:xstream (Maven): affected all versions; fixed in 1.4.15 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-2020-26258/ (Markdown: https://insights.sbomify.com/CVE-2020-26258/index.md) ``` ## Sources - CVE record: https://www.cve.org/CVERecord?id=CVE-2020-26258 - NVD: https://nvd.nist.gov/vuln/detail/CVE-2020-26258 - OSV: https://osv.dev/vulnerability/CVE-2020-26258 --- From sbomify Insights: https://insights.sbomify.com/CVE-2020-26258/ Summaries are generated and may contain mistakes; the official description above is the record.