CriticalCVE-2024-42009

    RoundCube Webmail Cross-Site Scripting Vulnerability (CVE-2024-42009)

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

    Share

    What is affected, what to do

    A Cross-Site Scripting (XSS) vulnerability in RoundCube Webmail allows a remote attacker to steal and relay a victim's emails using a crafted email message that exploits a Desanitization issue in message_body(). The attack can be executed remotely without authentication. The vulnerability is actively exploited in the wild, as evidenced by its inclusion in the CISA KEV catalog. Affected versions include RoundCube Webmail up to 1.6.7. An immediate upgrade to version 1.5.8 or higher is urgently recommended to mitigate this security risk.

    The vulnerability is being actively exploited; treat it as a priority. Update Roundcube Webmail to version 1.5.8, Roundcube Webmail to version 1.6.8. Immediate actions, mitigation and detection rules are in the runbook below.

    Affected
    • Roundcube Webmail lt *..1.5.8
    • Roundcube Webmail lt 1.6.0..1.6.8
    Fixed in
    • Roundcube Webmail 1.5.8
    • Roundcube Webmail 1.6.8

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

    Metrics

    9.3

    Priority

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

    Source: NVD, CVSS v3

    9.3

    CVSS v3

    Severity Critical on the scale from 0 to 10.

    Source: Debian, pwn.watch, CVE.org

    82.9 %

    EPSS score

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

    Source: FIRST EPSS, percentile 99.67

    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
    231.79 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 exploitedSource: ANSSI / CERT-FR How we classify
    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
    9.3 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
    9.3
    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
    82.9 %
    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
    99.67
    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: total
    Source: CISA Vulnrichment, as of 20 August 2025
    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-79

    Response and mitigation

    Why act now?

    Prioritisation rationale

    This CVE sits on KEV because it is network-reachable and requires no attacker authentication — delivering a crafted email is enough, with the victim merely opening it (UI:R). EPSS places it among the vulnerabilities most likely to be exploited; working PoCs are public and have been used in targeted campaigns against European mail infrastructure, both government-adjacent and civil-society. Treat any internet-exposed instance, and any deployment used by executives, IT admins, journalists or NGOs, as P1; VPN-only internal deployments can be P2 provided CSP and 2FA are enforced. No ransomware use has been reported — the impact profile is data theft (mail contents, session takeover, lateral phishing).

    1. Runbook step 1

      Immediate response (0-24 h)

      • Upgrade Roundcube to 1.5.8 (1.5.x branch) or 1.6.8 (1.6.x branch) immediately — the fix addresses the desanitization flaw in program/actions/mail/show.php. Check distro packages (Debian/Ubuntu DSA, RHEL/EPEL), as older OS repos often ship vulnerable builds.
      • If the patch window exceeds 24 h, gate the webmail UI behind a reverse proxy or WAF and restrict reachability to authenticated sessions from defined networks (VPN-only, EU geo-fencing).
      • Temporarily disable HTML mail rendering in Roundcube ($config['prefer_html'] = false;, $config['show_images'] = 0;) until the patch is deployed.
      • Invalidate all active sessions and force re-authentication (truncate/clear the temp/ session store or DELETE FROM session; in the Roundcube database), because existing sessions may already have been hijacked.
      • Scan inbound mail logs from the past 60 days for messages carrying suspicious SVG, <style>, <animate> payloads or on*= attributes in HTML parts (see detection section).
      • Audit admin/postmaster accounts for unauthorised forwarding rules, Sieve filters and API tokens — typical post-exploitation persistence after session theft.

    2. Runbook step 2

      Mitigation layers

      • Network segmentation: webmail frontend in a dedicated DMZ VLAN, no direct path to internal file servers or AD controllers; egress whitelisted to ports 25/587/465/993/143 only.
      • WAF rule: response-body inspection on the mail-show endpoint (_task=mail&_action=show); block responses containing javascript: URI schemes, data:text/html payloads or non-whitelisted <script>/<iframe> tags inside rendered mail HTML.
      • Enforce a strict Content-Security-Policy on the Roundcube UI: default-src 'self'; script-src 'self' 'nonce-...'; img-src 'self' data:; frame-ancestors 'none'; object-src 'none'; — contains XSS impact even against future desanitization bugs.
      • Harden session cookies: HttpOnly, Secure, SameSite=Strict ($config['session_samesite'] = 'Strict';) so that stolen cookies cannot be replayed cross-origin.
      • IAM hardening: mandatory 2FA plugin (kiss-2fa, twofactor_gauthenticator) for every account; privileged mail accounts in a separate auth realm.
      • Mail gateway: SpamAssassin/Rspamd rule for HTML mails containing obfuscated SVG/CDATA blocks and multiply-encoded entity sequences; raise score or quarantine.

    3. Runbook step 3

      Detection rules

      • Web access logs (nginx/Apache): a POST/GET to /?_task=mail&_action=compose arriving within seconds after _action=show from the same session — a strong signal of automated send-on-view via XSS payload. Sigma shape: selection: cs-uri-query|contains: '_action=show' followed by _action=compose under the same session cookie.
      • Zeek http.log / Suricata: inbound SMTP messages with a text/html MIME part containing <svg, <animate, xlink:href=javascript: or href="data:text/html — Suricata signature via file_data and pcre on these tokens.
      • Roundcube application logs (logs/errors.log, logs/sendmail.log): unusual sendmail entries outside normal business hours, especially to recipients outside the organisation's domain shortly after a mail/show request.
      • EDR / process telemetry on the webserver: php-fpm or httpd spawning sendmail/msmtp with atypical arguments or very large recipient counts.
      • SIEM correlation (KQL-style): WebLogs | where UriPath has '_task=mail' | summarize show=countif(Query has '_action=show'), compose=countif(Query has '_action=compose') by SessionId, bin(TimeGenerated,5m) | where compose > 0 and show > 0 and compose >= show.

    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

    A Cross-Site Scripting vulnerability in Roundcube through 1.5.7 and 1.6.x through 1.6.7 allows a remote attacker to steal and send emails of a victim via a crafted e-mail message that abuses a Desanitization issue in message_body() in program/actions/mail/show.php.

    Source: Debian Security Advisories, pwn.watch, NVD (NIST), cvelistv5, CISA KEV Catalog, 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
    • < 1.5.8
    • 1.6.0 – < 1.6.8
    • 1.5.8
    • 1.6.8

    Vendors and products

    Affected operating systems

    Affected operating systems
    Linuxdebianroundcubebookworm
    Linuxdebianroundcubebullseye

    Weakness classes (CWE)

    • CWE-79Improper Neutralization of Input During Web Page Generation ('Cross-site Scripting')

      Base

      The product does not neutralize or incorrectly neutralizes user-controllable input before it is placed in output that is used as a web page that is served to other users.

      Entry at MITRE CWE-79

    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
    ANSSI / CERT-FRLicence Ouverte 2.0, as of CERTFR-2024-ALE-010 – Multiples vulnérabilités dans Roundcube (clôturée 2024-10-07) (opens in a new tab)cert.cyber.gouv.fractively exploited

    References & sources

    • github.comroundcube/roundcubemail/releasesRelease notes
    • sonarsource.comblog/government-emails-at-risk-critical-cross-site-scripting-vu…Technical description, Third-party advisory
    • github.comroundcube/roundcubemail/releases/tag/1.5.8Release notes
    • github.comroundcube/roundcubemail/releases/tag/1.6.8Release notes
    • roundcube.netRoundcube advisory: Roundcube WebmailVendor advisory, pwn-watch
    • cisa.govknown-exploited-vulnerabilities-catalog?field_cve=CVE-2024-42009government-resource, US government resource
    • cert.cyber.gouv.frANSSI / CERT-FR: CERTFR-2024-ALE-010 – Multiples vulnérabilités dans Roundcube (clôturée 2024-10-07)cert-fr
    • pwn.watchpwn.watch: Roundcube Webmail: Webmail Cross-Site Scripting Vulnerabilitypwn-watch
    • NVD (NIST)NVD: CVE-2024-42009pwn-watch
    • cisa.govCISA Known Exploited Vulnerabilities Catalogpwn-watch

    Linked advisories

    Embed badge

    Show the severity and KEV status of this vulnerability on your site – with a link back here. The image is updated hourly.

    Badge preview for CVE-2024-42009
    <a href="https://intel.neosec.eu/en/cve/CVE-2024-42009"><img src="https://intel.neosec.eu/badge/cve/CVE-2024-42009.svg?lang=en" alt="CVE-2024-42009 – NEOSEC Intel" height="20"></a>