CriticalCVE-2026-76519

    Cisco Secure Email Gateway Arbitrary File Write Vulnerability (CVE-2026-76519)

    Published Last modified In CISA KEV since Sources: CERT-EU, CVE.org, BSI, Cisco PSIRT

    What is affected, what to do

    A vulnerability in the Advanced Malware Protection (AMP) feature of Cisco Secure Email Gateway could allow an unauthenticated, remote attacker to write arbitrary files on the underlying operating system. This vulnerability is due to improper handling of email attachments when the file reputation service is enabled.

    The vulnerability is being actively exploited; treat it as a priority. Update Secure Email Gateway to version 15.5.5-014. Immediate actions, mitigation and detection rules are in the runbook below.

    Affected
    • Cisco Secure Email eq 14.0.0-698..14.0.0-698
    • Cisco Secure Email eq 13.5.1-277..13.5.1-277
    • Cisco Secure Email eq 13.0.0-392..13.0.0-392
    • Cisco Secure Email eq 14.2.0-620..14.2.0-620
    • Cisco Secure Email eq 13.0.5-007..13.0.5-007
    • Cisco Secure Email eq 13.5.4-038..13.5.4-038
    • Cisco Secure Email eq 14.2.1-020..14.2.1-020
    • Cisco Secure Email eq 14.3.0-032..14.3.0-032
    • Cisco Secure Email eq 15.0.0-104..15.0.0-104
    • Cisco Secure Email eq 15.0.1-030..15.0.1-030
    • Cisco Secure Email eq 15.5.0-048..15.5.0-048
    • Cisco Secure Email eq 15.5.1-055..15.5.1-055
    • Cisco Secure Email eq 15.5.2-018..15.5.2-018
    • Cisco Secure Email eq 16.0.0-050..16.0.0-050
    • Cisco Secure Email eq 15.0.3-002..15.0.3-002
    • Cisco Secure Email eq 16.0.0-054..16.0.0-054
    • Cisco Secure Email eq 15.5.3-022..15.5.3-022
    • Cisco Secure Email eq 16.0.1-017..16.0.1-017
    • Cisco Secure Email eq 15.5.4-012..15.5.4-012
    • Cisco Secure Email eq 16.0.4-016..16.0.4-016
    • Cisco Secure Email eq 15.0.5-016..15.0.5-016
    • Cisco Secure Email eq 16.0.2-112..16.0.2-112
    • Cisco Secure Email eq 16.0.3-044..16.0.3-044

    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: CERT-EU, CVE.org, BSI, Cisco PSIRT

    1.6 %

    EPSS score

    Moderate — model estimates 1-10% exploitation likelihood.

    Source: FIRST EPSS, percentile 75.0

    Show all metrics
    Severity
    Critical
    Priority score

    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
    224.01
    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 (KEV)Source: VulnCheck KEV (opens in a new tab)
    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
    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
    1.6 %
    Moderate — model estimates 1-10% 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
    75.0
    High — this CVE ranks above the median of all CVEs scored today (rank ≥ 36%).
    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
    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-23

    Response and mitigation

    Why act now?

    Prioritisation rationale

    An email gateway is internet-facing by design. Exploitation needs no authentication and no user interaction: a single crafted email can give an attacker root on a system that sees all mail traffic, holds TLS keys and is wired into directory services. The modelled exploitation likelihood is only moderate and CISA does not flag ransomware use, but the KEV listing confirms real-world attacks, and gateways of this class are favoured targets for espionage and long-term persistence. Treat every vulnerable gateway with File Reputation enabled as critical — patch or mitigate within 24 hours. Gateways with AMP disabled are a lower priority but still belong in the emergency patch cycle.

    1. Runbook step 1

      Immediate response (0-24 h)

      • Inventory every affected system: Check all Cisco Secure Email Gateways (hardware, virtual, cloud) with the CLI version command. Affected releases are AsyncOS 15.0 through 15.5.5-014 and 16.0 through 16.5.0-780. A patch is available from the vendor — look up the fixed release in the Cisco Security Advisory and deploy it as an emergency change.
      • Confirm the exploit precondition: The flaw is only reachable when AMP File Reputation is enabled. Check Security Services > File Reputation and Analysis and the Incoming Mail Policies. A vulnerable box with File Reputation enabled goes to the top of the queue.
      • Stopgap if you cannot patch today: Temporarily disable File Reputation. You lose attachment malware scanning, so record the accepted risk and compensate downstream (see Mitigation layers).
      • Assess for compromise before patching: Export the configuration, mail_logs, AMP logs and audit logs off-box. Patching does not remove root access an attacker already has.
      • Rotate secrets if compromise is suspected: Rotate gateway admin accounts, LDAP bind accounts, SMTP AUTH credentials, TLS private keys and API tokens (e.g. SecureX/XDR and SIEM integrations). If compromise is confirmed, rebuild the appliance rather than trying to clean it.
      • Check reporting obligations: If you see evidence of exploitation, assess NIS2 reporting timelines (early warning within 24 h).

    2. Runbook step 2

      Mitigation layers

      • Network segmentation: Restrict management interfaces (HTTPS GUI, SSH, API) to a dedicated admin network. Allowlist the gateway's outbound traffic: DNS, update servers, AMP cloud and defined smarthosts. Block and log everything else. This makes reverse shells and data exfiltration harder after a successful exploit.
      • Upstream filtering: If you have an upstream filter (cloud mail filter or MTA), drop attachments whose names contain ../ or ..\ in the filename= or name= parameter. Cover RFC 2231 encoded variants (filename*=) and MIME encoded-word variants (=?utf-8?B?...?=).
      • IPS/network sensors: Write a Suricata rule for inbound SMTP on port 25 or 587, e.g. alert smtp any any -> $MAIL_GW 25 (msg:"Possible CVE-2026-76519 path traversal attachment"; content:"filename"; nocase; pcre:"/filename\*?=\s*\"?[^\r\n]*\.\.[\/\\]/i"; sid:...;). Effectiveness is limited where STARTTLS is not terminated upstream.
      • Appliance hardening: Disable unused services on the listeners. Move admin login to central authentication with MFA. Keep local accounts to a minimum.
      • Compensating controls while File Reputation is off: Rely on downstream malware scanning (M365/Exchange Online or Exchange) and endpoint protection. Temporarily route risky file types (archives, ISO, scripts) to quarantine via content filters.

    3. Runbook step 3

      Detection rules

      • Mail logs (syslog → SIEM): Search mail_logs and AMP logs for attachment names containing traversal sequences. SPL example: index=esa sourcetype=cisco:esa* ("../" OR "..\\" OR "%2e%2e" OR "filename*=") | stats count by src_ip, mail_from, attachment
      • Network telemetry (Zeek/NetFlow/firewall): Alert on new outbound connections from gateway IPs to destinations outside the allowlist, especially SSH, unusual high ports and long-lived sessions. KQL sketch: CommonSecurityLog | where SourceIP in (esa_ips) and DestinationIP !in (allowlist) | summarize count() by DestinationIP, DestinationPort
      • Gateway audit logs: Watch for unexpected configuration changes, new admin accounts, modified mail policies or message filters (e.g. BCC or forwarding rules), and logins from outside the admin network.
      • Integrity and behavioural anomalies: Watch for unexplained reboots, AMP process crashes, unusual CPU load or disk usage shortly after inbound mail with attachments. If you suspect compromise, engage Cisco TAC for forensics on the underlying OS — EDR is typically not available on the appliance.
      • Retro-hunt: Search back to at least 30 days before the KEV addition date (2026-10-14) for the patterns above.

    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 vulnerability in the Advanced Malware Protection (AMP) feature of Cisco Secure Email Gateway could allow an unauthenticated, remote attacker to write arbitrary files on the underlying operating system. This vulnerability is due to improper handling of email attachments when the file reputation service is enabled. An attacker could exploit this vulnerability by sending an email that contains a crafted attachment through an affected device. A successful exploit could allow the attacker to write arbitrary files and execute commands with root privileges on the underlying operating system.

    Source: certeu_advisory, NVD (NIST), BSI CSAF, BSI WID Portal, cvelistv5, CISA KEV Catalog, cisco_csaf, 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
    VendorProductAffected versionsFixed in
    CiscoCisco Secure Email
    • 13.0.0-392
    • 13.0.5-007
    • 13.5.1-277
    • 13.5.4-038
    • 14.0.0-698
    • 14.2.0-620
    • 14.2.1-020
    • 14.3.0-032
    • 15.0.0-104
    • 15.0.1-030
    • 15.0.3-002
    • 15.0.5-016
    • 15.5.0-048
    • 15.5.1-055
    • 15.5.2-018
    • 15.5.3-022
    • 15.5.4-012
    • 16.0.0-050
    • 16.0.0-054
    • 16.0.1-017
    • 16.0.2-112
    • 16.0.3-044
    • 16.0.4-016
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    CiscoSecure Email Gateway
    • < 15.5.5-014
    • < 16.5.0-780
    • 15.5.5-014
    • 16.5.0-780

    Affected operating systems

    Affected operating systems
    FamilyVendorProductVersion
    Otherciscoasyncos—

    Weakness classes (CWE)

    • CWE-23Relative Path Traversal

      Base

      The product uses external input to construct a pathname that should be within a restricted directory, but it does not properly neutralize sequences such as ".." that can resolve to a location that is outside of that directory.

      Entry at MITRE CWE-23

    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
    SourceReferenceMaturityPublished
    CISA KEV CatalogCISA Known Exploited Vulnerability (opens in a new tab)cisa.govactively exploited (KEV)
    PoC-in-GitHub (nomi-sec)CVE-2026-76519-POC (opens in a new tab)github.comPoC (publicly reported)reported, not verified

    References & sources

    Reanalysis & status changes

    Chronological NVD audit events for this CVE — reanalyses, CVSS updates, CPE diffs.

    1. Initial Analysisnvd@nist.gov

      • CPE Configuration: after AND OR *cpe:2.3:o:cisco:asyncos:*:*:*:*:*:*:*:* versions from (including) 15.0 up to (excluding) 15.5.5-014 *cpe:2.3:o:cisco:asyncos:*:*:*:*:*:*:*:* versions from (including) 16.0 up to (excluding) 16.5.0-780 OR cpe:2.3:a:cisco:secure_email_gateway_virtual_appliance_c100v:-:*:*:*:*:*:*:* cpe:2.3:a:cisco:secure_email_gateway_virtual_appliance_c300v:-:*:*:*:*:*:*:* cpe:2.3:a:cisco:secure_email_gateway_virtual_appliance_c600v:-:*:*:*:*:*:*:* cpe:2.3:h:cisco:secure_email_gateway_c195:-:*:*:*:*:*:*:* cpe:2.3:h:cisco:secure_email_gateway_c395:-:*:*:*:*:*:*:* cpe:2.3:h:cisco:secure_email_gateway_c695:-:*:*:*:*:*:*:*
      • Reference Type: after Cisco Systems, Inc.: https://sec.cloudapps.cisco.com/security/center/content/CiscoSecurityAdvisory/cisco-sa-esa-afw-zqYJkjxp Types: Vendor Advisory
      • Reference Type: after CISA-ADP: https://www.cisa.gov/known-exploited-vulnerabilities-catalog?field_cve=CVE-2026-76519 Types: US Government Resource

    2. CVE Modified134c704f-9b21-4f2e-91b3-4a467353bcc0

      • SSVC: before {"id":"CVE-2026-76519","role":"CISA Coordinator","options":[{"exploitation":"active"},{"automatable":"yes"},{"technic…
      • SSVC: after {"id":"CVE-2026-76519","role":"CISA Coordinator","options":[{"exploitation":"active"},{"automatable":"yes"},{"technic…

    3. CVE CISA KEV Update9119a7d8-5eab-497f-8521-727c672e3725

      • Date Added: after 2026-10-14
      • Due Date: after 2026-10-14
      • Required Action: after 2026-10-14
      • Vulnerability Name: after 2026-10-14

    4. CVE Modified134c704f-9b21-4f2e-91b3-4a467353bcc0

      • Reference: after https://www.cisa.gov/known-exploited-vulnerabilities-catalog?field_cve=CVE-2026-76519
      • SSVC: after {"id":"CVE-2026-76519","role":"CISA Coordinator","options":[{"exploitation":"active"},{"automatable":"yes"},{"technic…

    5. New CVE Receivedpsirt@cisco.com

      • Description: after A vulnerability in the Advanced Malware Protection (AMP) feature of Cisco Secure Email Gateway could allow an unauthenticated, remote attacker to write arbitrary files on the underlying operating system. This vulnerability is due to improper handling of email attachments when the file reputation service is enabled. An attacker could exploit this vulnerability by sending an email that contains a crafted attachment through an affected device. A successful exploit could allow the attacker to write arbitrary files and execute commands with&nbsp;root privileges on the underlying operating system.
      • CVSS V3.1: after AV:N/AC:L/PR:N/UI:N/S:U/C:H/I:H/A:H
      • CWE: after CWE-23
      • Affected: after New affected value received. <a href="https://github.com/CVEProject/cvelistV5/blob/main/cves/2026/76xxx/CVE-2026-76519.json">CVE-2026-76519</a>

    Linked advisories