CriticalCVE-2023-1671

    Sophos Web Appliance Command Injection Vulnerability (CVE-2023-1671)

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

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    What is affected, what to do

    A pre-auth command injection vulnerability in the warn-proceed handler of Sophos Web Appliance older than version 4.3.10.4 allows execution of arbitrary code.

    The vulnerability is being actively exploited; treat it as a priority. Update Sophos Web Appliance to version 4.3.10.4. Immediate actions, mitigation and detection rules are in the runbook below.

    Affected
    • Sophos Web Appliance lt *..4.3.10.4
    Fixed in
    • Sophos Web Appliance 4.3.10.4

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

    Metrics

    9.8

    Priority

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

    Source: NVD, CVSS v3

    9.8

    CVSS v3

    Severity Critical on the scale from 0 to 10.

    Source: pwn.watch, CVE.org

    —

    EPSS score

    No value is available for this vulnerability.

    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
    231.39 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.

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    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
    9.8 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
    9.8
    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.

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    99.99
    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.

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    CISA assessment (SSVC)
    Exploitation: active · automatable · Technical impact: total
    Source: CISA Vulnrichment, as of 28 January 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-77

    Response and mitigation

    Why act now?

    Prioritisation rationale

    This CVE is on KEV because it is remotely exploitable without authentication, yields root-level RCE on a perimeter appliance, and because the affected product was already end-of-life when the fix shipped — a textbook target for opportunistic scanners and initial access brokers. The exploitation likelihood ranks among the highest on KEV, and internet-wide scanning for the warn-proceed pattern has been continuous since disclosure. CISA has not flagged confirmed ransomware use, but a compromised SWA is a strategic pivot into the internal network, with TLS interception material and AD service accounts in reach — treat any internet-exposed SWA as a P1 incident until you can prove patch level 4.3.10.4+ or decommissioning.

    1. Runbook step 1

      Immediate response (0-24 h)

      • Upgrade Sophos Web Appliance (SWA) to 4.3.10.4 or later immediately — the vendor fix closes the pre-auth command injection in the warn-proceed handler.
      • Context that changes the decision: Sophos set SWA end-of-life on 20 July 2023. If the appliance is still deployed, start the migration to Sophos Firewall Web Protection or an alternative secure web gateway as a project track right now.
      • Remove the management interface (HTTPS/TCP 4444) and the user-facing proxy interface from the public internet. The flaw is pre-auth over HTTP(S); exposed instances are the primary target.
      • Move the appliance into an isolated management VLAN with strict ACLs. Block outbound traffic from the SWA to anything other than Sophos update infrastructure to kill reverse shells and C2 channels.
      • Preserve forensic evidence before patching: snapshot or image the appliance, export /var/log and configuration. If compromise is plausible, rebuild rather than patch — root-level pre-auth RCE cannot be cleared with a config review alone.
      • Rotate every credential used on or through the SWA: admin accounts, LDAP/AD bind accounts, API tokens, SNMP community strings, and TLS interception certificates.

    2. Runbook step 2

      Mitigation layers

      • Network segmentation: management plane reachable only via an admin jumphost network; proxy ports exposed only to internal client subnets, never from the internet.
      • Reverse proxy or WAF in front of the SWA: block requests that combine the warn-proceed parameter with shell metacharacters (;, |, `, $(, &&). Load Suricata/Snort signatures for CVE-2023-1671 (Emerging Threats ETPRO) and set them to alert+drop.
      • Egress filtering: from the SWA, allow only Sophos update destinations and required upstream resolvers. Explicitly deny common reverse-shell ports (TCP 4444, 1337, high ephemeral destinations).
      • Appliance hardening: disable unused admin protocols (SSH, SNMPv1/2), enforce strong admin passwords, and front the admin UI with MFA via an upstream IdP (SAML through a reverse proxy).
      • Monitoring baseline: capture HTTP methods, URIs, and user agents on an upstream tap (Zeek). Without this baseline, exploitation traces inside the HTTP body remain invisible.

    3. Runbook step 3

      Detection rules

      • Reverse-proxy access logs: POST requests to the warn-proceed endpoint containing URL-encoded shell metacharacters or Base64 blobs in the body. Sigma shape: selection: cs-uri-stem endswith 'index.php' AND cs-uri-query contains 'warn-proceed' AND cs-uri-query re '%3B|%7C|%24%28|%60'.
      • Network telemetry (Zeek/Suricata): new outbound TCP sessions from the SWA IP to destinations outside the Sophos update ASNs, especially on non-standard ports — a strong indicator of a reverse shell after successful RCE.
      • Appliance logs (/var/log/messages, audit log): process spawns from the web-server user (typically apache or nobody) into sh, bash, python, perl, curl, wget, nc. KQL shape once shipped to SIEM: ParentImage endswith "httpd" and Image matches "/(bash|sh|curl|wget|nc|python)/".
      • File-system monitoring: new or modified files in /tmp, /var/tmp, /dev/shm, and any changes under the web root (web-shell drop). Add file integrity monitoring to appliance binaries.
      • Downstream AD/LDAP authentication logs: unusual bind activity from the SWA service account outside policy-sync windows — a sign of credential abuse following appliance compromise.

    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 pre-auth command injection vulnerability in the warn-proceed handler of Sophos Web Appliance older than version 4.3.10.4 allows execution of arbitrary code.

    Source: 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
    SophosSophos Web Appliance
    • < 4.3.10.4
    • 4.3.10.4
    sophosweb_appliance
    • < 4.3.10.4
    • 4.3.10.4

    Vendors and products

    Weakness classes (CWE)

    • CWE-77Improper Neutralization of Special Elements used in a Command ('Command Injection')

      Class

      The product constructs all or part of a command using externally-influenced input from an upstream component, but it does not neutralize or incorrectly neutralizes special elements that could modify the intended command when it is sent to a downstream component.

      Entry at MITRE CWE-77

    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
    Packet StormSophos Web Appliance 4.3.10.4 Command Injection (opens in a new tab)packetstormsecurity.comPoC (publicly reported)reported, not verified—

    References & sources

    • sophos.comVendor advisory: Sophos Web ApplianceVendor advisory, pwn-watch
    • packetstormsecurity.comfiles/172016/Sophos-Web-Appliance-4.3.10.4-Command-Injection.ht…Exploit, Third-party advisory, Vulnerability database
    • cisa.govknown-exploited-vulnerabilities-catalog?field_cve=CVE-2023-1671government-resource, US government resource
    • pwn.watchpwn.watch: Sophos Web Appliance: Command Injection (CVE-2023-1671)pwn-watch
    • NVD (NIST)NVD: CVE-2023-1671pwn-watch
    • cisa.govCISA Known Exploited Vulnerabilities Catalogpwn-watch
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