CriticalCVE-2020-13965

    Roundcube Webmail Cross-Site Scripting (XSS) Vulnerability (CVE-2020-13965)

    Published In CISA KEV since Sources: pwn.watch, CVE.org, OSV

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    What is affected, what to do

    An issue was discovered in Roundcube Webmail before 1.3.12 and 1.4.x before 1.4.5. There is XSS via a malicious XML attachment because text/xml is among the allowed types for a preview.

    The vulnerability is being actively exploited; treat it as a priority. Update Roundcube Webmail to version 1.3.12, Roundcube Webmail to version 1.4.5. Immediate actions, mitigation and detection rules are in the runbook below.

    Affected
    • Roundcube Webmail lt *..1.3.12
    • Roundcube Webmail lt 1.4.0..1.4.5
    • Debian Linux eq 9.0..9.0
    • Debian Linux eq 10.0..10.0
    • Fedora eq 31..31
    • Fedora eq 32..32
    Fixed in
    • Roundcube Webmail 1.3.12
    • Roundcube Webmail 1.4.5

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

    Metrics

    6.3

    Priority

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

    Source: Vendor (CNA), CVSS v3

    6.1

    CVSS v3

    Severity Medium on the scale from 0 to 10.

    Source: pwn.watch, CVE.org, OSV

    76.6 %

    EPSS score

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

    Source: FIRST EPSS, percentile 99.54

    Show all metrics
    Severity
    Critical
    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
    209.77 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
    actively exploited
    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
    6.3 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
    6.1
    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
    76.6 %
    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
    99.54
    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
    Actively exploited
    Published
    In CISA KEV since

    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
    CISA assessment (SSVC)
    Exploitation: active · not automatable · Technical impact: partial
    Source: CISA Vulnrichment, as of 26 June 2024
    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-80

    Response and mitigation

    Why act now?

    Prioritisation rationale

    The bug needs user interaction (opening the attachment preview), but it can be delivered by email without authentication. Because of the scope change, the injected script runs in the victim's webmail session. That makes it a near-perfect spear-phishing primitive for mailbox harvesting, session theft and planting persistent forwarding rules. Roundcube XSS flaws are repeatedly used against government bodies, public administration, defence and critical-infrastructure organisations in Europe. Exploitation likelihood is very high, and CISA reports no known ransomware use. Despite the moderate base severity, NIS2-scoped organisations should treat internet-facing Roundcube as high priority and patch within 24–72 h. VPN-only internal instances can follow the regular, but prompt, patch cycle.

    1. Runbook step 1

      Immediate response (0-24 h)

      • Inventory: Identify every Roundcube instance, including forgotten test and hosting boxes. Check the version via "Settings → About" or RCMAIL_VERSION in program/include/iniset.php. All releases before 1.3.12 and 1.4.x before 1.4.5 are vulnerable.
      • Patch: Upgrade upstream installs to at least 1.3.12 (1.3 LTS branch) or 1.4.5. Both branches have since accumulated further security issues, so moving to a currently supported Roundcube release is strongly recommended.
      • Update distribution packages: Update Debian 9/10, Fedora 31/32 and Bitnami Roundcube images (1.4.0) through the package manager or by rebuilding the image. Look up the fixed package version in the respective distribution security advisory. Debian 9 and Fedora 31/32 are end-of-life, so plan a migration.
      • Restrict exposure: If patching within 24 h is not feasible, move webmail behind VPN or a reverse proxy enforcing pre-authentication (SSO/MFA).
      • Compromise check: Prioritise review of accounts that show signs of having opened XML attachments (see detection). Check forwarding rules, Sieve filters, identities and signatures. If anything looks off, kill sessions and reset passwords.

    2. Runbook step 2

      Mitigation layers

      • Configuration: Remove text/xml and application/xml from the browser-inline MIME list (client_mimetypes in config/config.inc.php). Then verify that XML attachments are only offered as downloads.
      • Mail gateway/content filter: Quarantine externally sourced attachments with text/xml/application/xml content type or a .xml extension where there is no business need. Treat as especially suspicious any that contain the XHTML namespace (http://www.w3.org/1999/xhtml), <script, onload=, onerror= or javascript:.
      • WAF/reverse proxy: Rewrite responses from the Roundcube _action=get endpoint carrying Content-Type: text/xml to Content-Disposition: attachment, or block them outright. Also enforce a strict Content-Security-Policy (script-src 'self', no unsafe-inline for attachment frames) plus X-Content-Type-Options: nosniff.
      • Session hardening: Set cookies with Secure, HttpOnly and SameSite=Strict. Enable session IP binding (ip_check = true) to make stolen sessions harder to reuse.
      • Least privilege: Restrict plugins such as managesieve for regular users, or block external forwarding at the MTA policy level. This stops an XSS from turning into persistent mailbox exfiltration.

    3. Runbook step 3

      Detection rules

      • Web server access logs: Look for hits on _task=mail&_action=get with _mimetype=text/xml (or an XML _mimeclass), or with _frame=1/_embed=1 on XML parts. SPL sketch: index=web uri_query="*_action=get*" (uri_query="*text%2Fxml*" OR uri_query="*xml*") | stats count by src_ip, user.
      • Mail gateway logs: External messages with XML attachments sent to multiple mailboxes, especially executives or admins. Sigma shape: attachment_mime|contains: 'xml' AND attachment_content|contains: ['xhtml', '<script', 'onerror='].
      • Post-exploitation in webmail: Watch for the same session issuing _action=save-prefs, _action=plugin.managesieve-save, identity edits, or bulk _action=export/_action=fetch shortly after an XML attachment request.
      • Network telemetry (Zeek/Suricata): Client browsers beaconing to unfamiliar domains right after Roundcube attachment views. Also flag the same session ID appearing from new source IPs (session hijacking).
      • IMAP/MTA logs: Newly created forwards to external addresses, or sudden spikes in outbound mail from individual accounts.

    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
    Actively exploited: treat the vulnerability as a priority in vulnerability handling under Art. 21(2)(e) NIS2. If it is exploited in your environment, check the reporting obligation under Art. 23 (early warning within 24 hours).
    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
    Since 11.09.2026, manufacturers of affected products with digital elements must report actively exploited vulnerabilities under Art. 14 CRA, with an early warning within 24 hours via ENISA's single reporting platform.
    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

    An issue was discovered in Roundcube Webmail before 1.3.12 and 1.4.x before 1.4.5. There is XSS via a malicious XML attachment because text/xml is among the allowed types for a preview.

    Source: pwn.watch, NVD (NIST), cvelistv5, CISA KEV Catalog, OSV (Open Source Vulnerabilities), CVE.org (MITRE)

    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
    roundcubewebmail
    • 1.4.0 – < 1.4.5
    • < 1.3.12
    • 1.4.5
    • 1.3.12
    Distribution and container packages (1)

    Downstream packages (e.g. Bitnami, Debian, Ubuntu, Red Hat). Versions refer to the distribution, not the vendor.

    Distribution and container packages
    Affected versionsFixed in
    bitnamiroundcube
    • 1.4.0
    • —

    Vendors and products

    Affected operating systems

    Affected operating systems
    Linuxdebiandebian_linux10.0
    Linuxdebiandebian_linux9.0
    Otherfedoraprojectfedora31
    Otherfedoraprojectfedora32

    Weakness classes (CWE)

    • CWE-80Improper Neutralization of Script-Related HTML Tags in a Web Page (Basic XSS)

      Variant

      The product receives input from an upstream component, but it does not neutralize or incorrectly neutralizes special characters such as "<", ">", and "&" that could be interpreted as web-scripting elements when they are sent to a downstream component that processes web pages.

      Entry at MITRE CWE-80

    Public exploit references

    Publicly reported proof-of-concepts, exploit modules and detection templates for this vulnerability. NEOSEC links to the original sources only and does not provide any exploit code.

    Public exploit references
    CISA KEV CatalogCISA Known Exploited Vulnerability (opens in a new tab)cisa.govactively exploited
    Reference tagged as exploitgithub.com (opens in a new tab)PoC (publicly reported)reported, not verified—

    References & sources

    • github.comDrunkenShells/Disclosures/tree/master/CVE-2020-13965-Cross Site…web, x_refsource_MISC, Exploit, Third-party advisory
    • github.comroundcube/roundcubemail/commit/884eb611627ef2bd5a2e20e02009ebb1…web, x_refsource_MISC, Patch, Third-party advisory
    • github.comroundcube/roundcubemail/compare/1.4.4...1.4.5web, x_refsource_MISC, Patch
    • github.comroundcube/roundcubemail/releases/tag/1.3.12web, x_refsource_MISC, Release notes
    • github.comroundcube/roundcubemail/releases/tag/1.4.5web, x_refsource_MISC, Release notes
    • lists.fedoraproject.orgFEDORA-2020-2a1a6a8432web, Vendor advisory, x_refsource_FEDORA, Mailing list
    • lists.fedoraproject.orgFEDORA-2020-aeffd92b77web, Vendor advisory, x_refsource_FEDORA, Mailing list
    • roundcube.netRoundcube advisory: CVE-2020-13965web, x_refsource_CONFIRM, Vendor advisory, pwn-watch
    • debian.orgDSA-4700web, Vendor advisory, x_refsource_DEBIAN, Third-party advisory
    • cisa.govknown-exploited-vulnerabilities-catalog?field_cve=CVE-2020-13965government-resource, US government resource
    • pwn.watchpwn.watch: Roundcube Webmail Cross-Site Scripting (XSS)pwn-watch
    • NVD (NIST)NVD: CVE-2020-13965pwn-watch
    • cisa.govCISA Known Exploited Vulnerabilities Catalogpwn-watch
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