HighCVE-2020-26258

    Server-Side Forgery Request can be activated unmarshalling with XStream (CVE-2020-26258)

    Published Last modified Sources: Red Hat, Debian, CVE.org, OSV

    What is affected, what to do

    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.

    Update Xstream to version 1.4.15.

    Affected
    • Xstream lt *..1.4.15
    Fixed in
    • Xstream 1.4.15

    Not sure whether and how you are affected? Ask a question about this vulnerability

    Metrics

    7.7

    Priority

    XIEM Effective CVSS: highest available CVSS rating from NVD and vendor data.

    Source: NVD, CVSS v3

    6.3

    CVSS v3

    Severity Medium on the scale from 0 to 10.

    Source: Red Hat, Debian, CVE.org, OSV

    81.8 %

    EPSS score

    High — model estimates ≥ 50% chance of real-world exploitation within 30 days.

    Source: FIRST EPSS, percentile 99.64

    Show all metrics
    Severity
    High
    Priority (0–325)

    The priority score is a consolidated metric that condenses several individual signals into a single, action-guiding ranking: technical severity (CVSS), exploitation likelihood (EPSS), known-exploited status (KEV) and the context of the affected asset. The aim is to answer the only truly important question in vulnerability management: what first?

    Read in glossary
    110.93 Methodology
    Exploit maturity

    An exploit is code or a technique that specifically uses a concrete vulnerability to force unintended behaviour — such as executing code or escalating privileges. It is the tool that turns a theoretical flaw into a practical attack.

    Read in glossary
    no public PoC known
    XIEM Effective CVSS

    XIEM® is the tiered managed-security operating model from NEOSEC and a registered trademark of NEOSEC GmbH. It extends classic SIEM — the central collection, normalisation and correlation of security-relevant events — with endpoint forensics, network visibility and deception technology, and consolidates them into three building tiers: Sentry, Orchestrate and Command.

    Read in glossary
    7.7 Methodology
    CVSS v3

    CVSS is the globally established, open standard for assessing the technical severity of a vulnerability on a scale from 0 to 10. It describes how easily a flaw can be exploited and what damage it can cause — but not how likely its actual exploitation is. CVSS and the complementary EPSS deliberately answer different questions.

    Read in glossary
    6.3
    EPSS score

    The EPSS score is the absolute model output for an individual vulnerability: the estimated probability of real-world exploitation within the next 30 days, expressed as a value between 0 and 1 (i.e. 0 % to 100 %). A score of 0.42 means „the model estimates a 42 % chance of real-world exploitation within 30 days“.

    Read in glossary
    81.8 %
    High — model estimates ≥ 50% chance of real-world exploitation within 30 days.
    EPSS percentile

    The EPSS percentile is the relative position of a vulnerability within all EPSS-scored CVEs, expressed as a value between 0 and 1. A percentile of 0.90 means „this CVE has a higher EPSS score than 90 % of all other scored CVEs“. Unlike the EPSS score, it is not a probability — but a positioning within a ranking.

    Read in glossary
    99.64
    Critical — this CVE ranks in the top fifth of all CVEs scored today (rank ≥ 80%).
    KEV status

    The KEV catalogue is a list maintained by the US authority CISA of vulnerabilities for which active exploitation in the wild has been confirmed. It answers not the question „how severe?“ but „is it already being attacked?“ — thereby sharply prioritising patching.

    Read in glossary
    —
    Published
    CISA assessment (SSVC)
    Exploitation: none known · automatable · Technical impact: partial
    Source: CISA Vulnrichment, as of 7 October 2026
    CWE

    CWE is a catalogue of typical weakness types in software and hardware — such as flawed input validation, unsafe memory handling or poor authentication. Where a CVE names a concrete vulnerability in a concrete product, a CWE describes the underlying class of defect.

    Read in glossary
    CWE-918

    Detection rules

    No NEOSEC detection rule is available for this vulnerability yet.

    Classification under NIS2 and CRA

    Rule-based classification from exploitation status and severity. It does not replace a case-by-case assessment.

    NIS2

    NIS2 is EU Directive (EU) 2022/2555 to raise the level of cybersecurity across the Union. It substantially broadens obligations compared with the first NIS directive: more sectors, mandatory risk management, staged reporting duties and personal accountability of senior management.

    Read in glossary
    High technical severity: assess and remediate the vulnerability in vulnerability handling under Art. 21(2)(e) NIS2 and document the decision.
    CRA

    The CRA is EU Regulation (EU) 2024/2847 setting horizontal cybersecurity requirements for „products with digital elements“ — from industrial controllers and software to connected consumer devices. For the first time manufacturers must ensure security across the entire product lifecycle, handle vulnerabilities and provide security updates.

    Read in glossary
    From 11.12.2027, Annex I Part II CRA requires manufacturers of affected products with digital elements to handle vulnerabilities without delay and provide security updates.
    ISO/IEC 27001

    ISO/IEC 27001 is the internationally leading standard for an information security management system (ISMS). It describes a risk-based, process-oriented framework to systematically plan, implement, review and improve information security.

    Read in glossary
    Control A.8.8, management of technical vulnerabilities: assess relevance to your systems, plan remediation and keep evidence.

    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.

    Source: redhat_csaf, Debian Security Advisories, cvelistv5, NVD (NIST), OSV (Open Source Vulnerabilities)

    Affected products

    The following versions are affected. Older releases of the same product line are also vulnerable unless stated otherwise.

    Affected products
    Affected versionsFixed in
    x-streamxstream
    • < 1.4.15
    • 1.4.15
    apachestruts
    • < 6.0.0
    • 6.0.0
    xstreamxstream
    • < 1.4.15
    • 1.4.15

    Vendors and products

    Affected operating systems

    Affected operating systems
    Linuxdebiandebian_linux10.0
    Linuxdebiandebian_linux9.0
    Linuxdebianlibxstream-javabuster
    Otherfedoraprojectfedora33
    Otherfedoraprojectfedora34
    Otherfedoraprojectfedora35

    Weakness classes (CWE)

    • CWE-918Server-Side Request Forgery (SSRF)

      Base

      The web server receives a URL or similar request from an upstream component and retrieves the contents of this URL, but it does not sufficiently ensure that the request is being sent to the expected destination.

      Entry at MITRE CWE-918

    References & sources

    Changes to this CVE

    Who changed this CVE and when: NVD (analysis, affected products, CVSS), the CVE publisher (CNA) and additional providers such as CISA (ADP).

    1. Record modifiedGitHub

      Show 27 original changes
      Individual changes of this event as published by NVD
      TypeActionBeforeAfter
      Referenceadded
      —
      https://github.com/x-stream/xstream/security/advisories/GHSA-4cch-wxpw-8p28
      Referenceadded
      —
      https://lists.apache.org/thread.html/r97993e3d78e1f5389b7b172ba9f308440830ce5f051ee62714a0aa34@%3Ccommits.struts.apache.org%3E
      Referenceadded
      —
      https://lists.debian.org/debian-lts-announce/2020/12/msg00042.html
      Referenceadded
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      https://lists.fedoraproject.org/archives/list/package-announce@lists.fedoraproject.org/message/22KVR6B5IZP3BGQ3HPWIO2FWWCKT3DHP
      Referenceadded
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      https://lists.fedoraproject.org/archives/list/package-announce@lists.fedoraproject.org/message/PVPHZA7VW2RRSDCOIPP2W6O5ND254TU7
      Referenceadded
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      https://lists.fedoraproject.org/archives/list/package-announce@lists.fedoraproject.org/message/QGXIU3YDPG6OGTDHMBLAFN7BPBERXREB
      Referenceadded
      —
      https://security.netapp.com/advisory/ntap-20210409-0005
      Referenceadded
      —
      https://www.debian.org/security/2021/dsa-4828
      Referenceadded
      —
      https://x-stream.github.io/CVE-2020-26258.html
      Referenceremoved
      https://github.com/x-stream/xstream/security/advisories/GHSA-4cch-wxpw-8p28
      —
      Referenceremoved
      https://lists.apache.org/thread.html/r97993e3d78e1f5389b7b172ba9f308440830ce5f051ee62714a0aa34@%3Ccommits.struts.apache.org%3E
      —
      Referenceremoved
      https://lists.debian.org/debian-lts-announce/2020/12/msg00042.html
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      Referenceremoved
      https://lists.fedoraproject.org/archives/list/package-announce@lists.fedoraproject.org/message/22KVR6B5IZP3BGQ3HPWIO2FWWCKT3DHP
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      Referenceremoved
      https://lists.fedoraproject.org/archives/list/package-announce@lists.fedoraproject.org/message/PVPHZA7VW2RRSDCOIPP2W6O5ND254TU7
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      https://lists.fedoraproject.org/archives/list/package-announce@lists.fedoraproject.org/message/QGXIU3YDPG6OGTDHMBLAFN7BPBERXREB
      —
      Referenceremoved
      https://security.netapp.com/advisory/ntap-20210409-0005
      —
      Referenceremoved
      https://www.debian.org/security/2021/dsa-4828
      —
      Referenceremoved
      https://x-stream.github.io/CVE-2020-26258.html
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      Reference typeremoved
      https://github.com/x-stream/xstream/security/advisories/GHSA-4cch-wxpw-8p28 Types: Mitigation, Third Party Advisory
      —
      Reference typeremoved
      https://lists.apache.org/thread.html/r97993e3d78e1f5389b7b172ba9f308440830ce5f051ee62714a0aa34@%3Ccommits.struts.apache.org%3E Types: Issue Tracking, Mailing List
      —
      Reference typeremoved
      https://lists.debian.org/debian-lts-announce/2020/12/msg00042.html Types: Mailing List, Third Party Advisory
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      Reference typeremoved
      https://lists.fedoraproject.org/archives/list/package-announce@lists.fedoraproject.org/message/22KVR6B5IZP3BGQ3HPWIO2FWWCKT3DHP Types: Mailing List
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      Reference typeremoved
      https://lists.fedoraproject.org/archives/list/package-announce@lists.fedoraproject.org/message/PVPHZA7VW2RRSDCOIPP2W6O5ND254TU7 Types: Mailing List
      —
      Reference typeremoved
      https://lists.fedoraproject.org/archives/list/package-announce@lists.fedoraproject.org/message/QGXIU3YDPG6OGTDHMBLAFN7BPBERXREB Types: Mailing List
      —
      Reference typeremoved
      https://security.netapp.com/advisory/ntap-20210409-0005 Types: Third Party Advisory
      —
      Reference typeremoved
      https://www.debian.org/security/2021/dsa-4828 Types: Third Party Advisory
      —
      Reference typeremoved
      https://x-stream.github.io/CVE-2020-26258.html Types: Exploit, Mitigation, Third Party Advisory
      —

      Source identifier: security-advisories@github.com

    2. Record modifiedCISA ADP

      CISA assessment (SSVC): exploitation: none known, automatable: yes

      Show the original change
      Individual changes of this event as published by NVD
      TypeActionBeforeAfter
      SSVC assessmentadded
      —
      {"id":"CVE-2020-26258","role":"CISA Coordinator","options":[{"exploitation":"none"},{"automatable":"yes"},{"technicalImpact":"partial"}],"version":"2.0.3","timestamp":"2026-10-07T18:41:22.362836Z"}

      Source identifier: 134c704f-9b21-4f2e-91b3-4a467353bcc0

    3. Record modifiedCVE Program

      Show 27 original changes
      Individual changes of this event as published by NVD
      TypeActionBeforeAfter
      Referenceadded
      —
      https://github.com/x-stream/xstream/security/advisories/GHSA-4cch-wxpw-8p28
      Referenceadded
      —
      https://lists.apache.org/thread.html/r97993e3d78e1f5389b7b172ba9f308440830ce5f051ee62714a0aa34%40%3Ccommits.struts.apache.org%3E
      Referenceadded
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      https://lists.debian.org/debian-lts-announce/2020/12/msg00042.html
      Referenceadded
      —
      https://lists.fedoraproject.org/archives/list/package-announce%40lists.fedoraproject.org/message/22KVR6B5IZP3BGQ3HPWIO2FWWCKT3DHP/
      Referenceadded
      —
      https://lists.fedoraproject.org/archives/list/package-announce%40lists.fedoraproject.org/message/PVPHZA7VW2RRSDCOIPP2W6O5ND254TU7/
      Referenceadded
      —
      https://lists.fedoraproject.org/archives/list/package-announce%40lists.fedoraproject.org/message/QGXIU3YDPG6OGTDHMBLAFN7BPBERXREB/
      Referenceadded
      —
      https://security.netapp.com/advisory/ntap-20210409-0005/
      Referenceadded
      —
      https://www.debian.org/security/2021/dsa-4828
      Referenceadded
      —
      https://x-stream.github.io/CVE-2020-26258.html
      Referenceremoved
      https://github.com/x-stream/xstream/security/advisories/GHSA-4cch-wxpw-8p28
      —
      Referenceremoved
      https://lists.apache.org/thread.html/r97993e3d78e1f5389b7b172ba9f308440830ce5f051ee62714a0aa34%40%3Ccommits.struts.apache.org%3E
      —
      Referenceremoved
      https://lists.debian.org/debian-lts-announce/2020/12/msg00042.html
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      Referenceremoved
      https://lists.fedoraproject.org/archives/list/package-announce%40lists.fedoraproject.org/message/22KVR6B5IZP3BGQ3HPWIO2FWWCKT3DHP/
      —
      Referenceremoved
      https://lists.fedoraproject.org/archives/list/package-announce%40lists.fedoraproject.org/message/PVPHZA7VW2RRSDCOIPP2W6O5ND254TU7/
      —
      Referenceremoved
      https://lists.fedoraproject.org/archives/list/package-announce%40lists.fedoraproject.org/message/QGXIU3YDPG6OGTDHMBLAFN7BPBERXREB/
      —
      Referenceremoved
      https://security.netapp.com/advisory/ntap-20210409-0005/
      —
      Referenceremoved
      https://www.debian.org/security/2021/dsa-4828
      —
      Referenceremoved
      https://x-stream.github.io/CVE-2020-26258.html
      —
      Reference typeremoved
      https://github.com/x-stream/xstream/security/advisories/GHSA-4cch-wxpw-8p28 Types: Mitigation, Third Party Advisory
      —
      Reference typeremoved
      https://lists.apache.org/thread.html/r97993e3d78e1f5389b7b172ba9f308440830ce5f051ee62714a0aa34%40%3Ccommits.struts.apache.org%3E Types: Issue Tracking, Mailing List
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      Reference typeremoved
      https://lists.debian.org/debian-lts-announce/2020/12/msg00042.html Types: Mailing List, Third Party Advisory
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      Reference typeremoved
      https://lists.fedoraproject.org/archives/list/package-announce%40lists.fedoraproject.org/message/22KVR6B5IZP3BGQ3HPWIO2FWWCKT3DHP/ Types: Mailing List
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      Reference typeremoved
      https://lists.fedoraproject.org/archives/list/package-announce%40lists.fedoraproject.org/message/PVPHZA7VW2RRSDCOIPP2W6O5ND254TU7/ Types: Mailing List
      —
      Reference typeremoved
      https://lists.fedoraproject.org/archives/list/package-announce%40lists.fedoraproject.org/message/QGXIU3YDPG6OGTDHMBLAFN7BPBERXREB/ Types: Mailing List
      —
      Reference typeremoved
      https://security.netapp.com/advisory/ntap-20210409-0005/ Types: Third Party Advisory
      —
      Reference typeremoved
      https://www.debian.org/security/2021/dsa-4828 Types: Third Party Advisory
      —
      Reference typeremoved
      https://x-stream.github.io/CVE-2020-26258.html Types: Exploit, Mitigation, Third Party Advisory
      —

      Source identifier: af854a3a-2127-422b-91ae-364da2661108

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