Sophos XG Firewall Buffer Overflow Vulnerability (CVE-2020-15069)
Published In CISA KEV since Sources: pwn.watch, CVE.org
What is affected, what to do
Sophos XG Firewall 17.x through v17.5 MR12 allows a Buffer Overflow and remote code execution via the HTTP/S Bookmarks feature for clientless access. Hotfix HF062020.1 was published for all firewalls running v17.x.
The vulnerability is being actively exploited; treat it as a priority. The available sources name no fixed version. Check the vendor guidance in the references below. Immediate actions, mitigation and detection rules are in the runbook below.
Conflicting version data — version display is hidden until the data is resolved.
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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
10.7 %
EPSS score
Elevated — model estimates 10-50% exploitation likelihood.
Source: FIRST EPSS, percentile 95.8
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- 222.45 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- 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 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- 10.7 %
- Elevated — model estimates 10-50% exploitation likelihood.
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- 95.8
- 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 · automatable · Technical impact: total
- Source: CISA Vulnrichment, as of 7 February 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-120
Response and mitigation
Why act now?
Prioritisation rationale
This flaw is reachable over the network without authentication or user interaction and gives full code execution on a perimeter device. An attacker who exploits it owns the network edge and can intercept traffic, harvest credentials and pivot inside. Its late addition to KEV, years after disclosure, shows that attackers actively hunt for unpatched legacy edge appliances. CISA lists no known ransomware use, but the likelihood of exploitation remains well above average. Treat any remaining v17.x instance with a reachable User Portal as critical and remediate it immediately under your NIS2 risk-management obligations. Internally reachable units without Clientless Access can follow, but should still be migrated promptly.
Runbook step 1
Immediate response (0-24 h)
- Inventory: Identify every Sophos XG Firewall running firmware 17.x up to and including v17.5 MR12. Prioritise devices that expose the User Portal to the internet and have Clientless Access enabled.
- Verify the hotfix: Confirm that hotfix HF062020.1 is installed. Hotfix status is shown in WebAdmin under Backup & Firmware. If automatic hotfix installation was disabled, apply the hotfix manually now.
- Plan the upgrade: v17.x is a legacy release. Migrate to a current, vendor-supported SFOS version — look up the target version in the vendor advisory.
- Disable the feature: If you cannot patch immediately, disable HTTP/S bookmarks for Clientless Access. Also remove User Portal access from the WAN zone (Device Access: untick User Portal for WAN).
- Check for compromise: On any device that was exposed before the hotfix, review the configuration for unknown admin accounts and altered firewall rules, NAT entries and VPN profiles. Then rotate all local admin and portal credentials, along with any LDAP/AD bind accounts.
Runbook step 2
Mitigation layers
- Exposure and segmentation: Do not expose the User Portal or WebAdmin to the internet. Depending on configuration these typically run on TCP 443 and 4444. Allow access only via VPN or from an allowlist of fixed source IPs.
- Alternative remote access: Replace Clientless Access with SSL VPN or IPsec with MFA until the device is patched or migrated.
- Upstream IPS/WAF: In front of the firewall, drop User Portal requests with abnormally long parameter values or request bodies. A Suricata rule could be shaped as
http.method; content:"POST"; http.request_body; isdataat:<threshold>,relative;, scoped to the portal host. Set the threshold from a baseline of legitimate bookmark traffic. - Egress control: Restrict connections that originate from the firewall itself to the destinations it needs: Sophos update servers, NTP, DNS and syslog. Block and log everything else on an upstream device.
- IAM: Keep the number of admin accounts to a minimum and enforce MFA on WebAdmin and the User Portal. Scope LDAP bind accounts to least privilege.
- Logging: Forward all firewall logs to the SIEM via syslog, so evidence survives if the appliance itself is compromised.
Runbook step 3
Detection rules
- User Portal access logs: Look for requests to bookmark or clientless functions with oversized parameters, unusual byte sequences, or bursts of 5xx responses. SPL starting point:
index=sophos sourcetype=*userportal* (bookmark OR clientless) | where len(uri)>1024 OR bytes_in>10000. - Network telemetry (Zeek/Suricata): Alert on new outbound connections from the firewall's management or WAN IP to destinations you have not seen before. Pay particular attention to long-lived shell-like sessions and HTTP downloads. Zeek starting point:
conn.logwhereid.orig_h == <fw_ip>andid.resp_his not on the allowlist. - Configuration and admin events: In the admin and event logs, watch for new users, privilege changes, disabled hotfix auto-install, new firewall or NAT rules, and logins from unfamiliar ranges. Sigma shape:
logsource: product: sophos_xg, service: adminwithselection: event: (user_added|rule_added|config_change). - Service instability: Unexpected web service crashes or restarts in the appliance system log can indicate failed overflow attempts. Correlate them with the timing of portal requests.
- Pivot into the internal network: Hunt for lateral movement that originates from the firewall's internal IP. Look for Windows Event ID 4624 (logon type 3/10) with the firewall IP as source, and Sysmon EID 3 connections from the firewall to SMB or RDP.
- User Portal access logs: Look for requests to bookmark or clientless functions with oversized parameters, unusual byte sequences, or bursts of 5xx responses. SPL starting point:
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
Sophos XG Firewall 17.x through v17.5 MR12 allows a Buffer Overflow and remote code execution via the HTTP/S Bookmarks feature for clientless access. Hotfix HF062020.1 was published for all firewalls running v17.x.
Source: pwn.watch, cvelistv5, NVD (NIST), CISA KEV Catalog, CVE.org (MITRE)
Vendors and products
Affected operating systems
| Other | sophos | xg_firewall_firmware | 17.5 |
| Other | sophos | xg_firewall_firmware | — |
Weakness classes (CWE)
CWE-120Buffer Copy without Checking Size of Input ('Classic Buffer Overflow')
Base
The product copies an input buffer to an output buffer without verifying that the size of the input buffer is less than the size of the output buffer.
Entry at MITRE CWE-120
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.
| CISA KEV Catalog | CISA Known Exploited Vulnerability (opens in a new tab)cisa.gov | actively exploited |
References & sources
- community.sophos.comSophos advisory: Sophos XG Firewallx_refsource_CONFIRM, Mitigation, Vendor advisory, pwn-watch
- cisa.govknown-exploited-vulnerabilities-catalog?field_cve=CVE-2020-15069government-resource, US government resource
- pwn.watchpwn.watch: Sophos XG Firewall: XG Firewall Buffer Overflow Vulnerabilitypwn-watch
- NVD (NIST)NVD: CVE-2020-15069pwn-watch
- cisa.govCISA Known Exploited Vulnerabilities Catalogpwn-watch
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