CVE-2026-96656 Plex · Media Server

Plex Media Server - Arbitrary File Write

Vulnerability at a glance

Severity, exploitation likelihood & attack requirements

CVSS v4.0 severity
8.6High
EPSS · exploitation likelihood
0.816% Probability within 30 daysPercentile 56.7
EPSS trend
Unchanged Since 2026-10-22
Known exploitation
Known exploited CISA KEV catalog
Attack vector
NetworkRemotely reachable
Attack complexity
LowFewer obstacles to exploitation
Privileges required
HighElevated privileges required
User interaction
NoneNo user action needed
Exploit availability & maturity
Not scored Availability not established No explicit exploit maturity assessment View exploit evidence
How to read the colors & trend
Higher exposureElevatedModerateLower exposureUnknown / unassessed

CVSS colors follow its reported severity. Attack-factor colors describe each requirement, not an overall risk rating. Gray also covers absence from KEV; absence does not establish safety.

EPSS display bands: below 1% blue, 1–10% amber, 10–50% orange, 50% and above red. These are presentation bands, not FIRST severity categories. The trend compares daily EPSS probabilities, not percentile ranks; “pp” means percentage points. The sparkline shows relative movement, with its vertical scale fitted to the observed scores.

Already protected by existing Atomicorp rules No new CVE-specific rule required.

Atomicorp ModSecurity protection

Protected by Atomicorp rules

Atomicorp ModSecurity rules block attacks exploiting this vulnerability. Keep your rules current.

By targeting underlying attack techniques and CWE weakness classes, existing rules can protect against newly disclosed vulnerabilities. Rule changes are regression-tested against attack and false-positive corpora.

1 rule identified View rules & research details →

WAF protection does not change the CVSS or EPSS score. Keep your software patched and your Atomicorp rules current.

CISA SSVC assessment

CISA ADP · Assessed 2026-10-20 · SSVC 2.0.3

Exploitation
Active exploitation
Automatable
No
Technical Impact
Total

Stakeholder-Specific Vulnerability Categorization records CISA’s assessment of exploitation, automation, and technical impact. “None reported” reflects the assessment date; it does not establish that no exploit exists. View SSVC source details.

On this page

Atomicorp protection

Rule 398125 blocks arbitrary file write attempts associated with CVE-2026-96656. It is recorded here as a reviewed blocking rule.

This rule association comes from an engineering review of the deployed protection. The publication records this finding as reviewed protection.

Vulnerability and exploitation context

CVE-2026-96656 affects Plex Media Server. Plex describes the security issues and their remediation in its security advisory .

CISA lists all four related vulnerabilities—CVE-2026-96652, CVE-2026-96654, CVE-2026-96655 and CVE-2026-96656—in its Known Exploited Vulnerabilities catalog. CISA announced their addition on October 20, 2026, based on evidence of active exploitation. Prioritize the vendor update and follow Plex’s incident-response guidance.

CVE Details

  • Protection status: Protected by Atomicorp rules · About protection statuses
  • CVE: CVE-2026-96656
  • Name: Plex Media Server - Arbitrary File Write
  • Severity: High
  • CVSS: 8.6 (v4.0) (High)
  • CVSS version: 4.0
  • CVSS source: cisa-cg CNA
  • CVSS vector: CVSS:4.0/AV:N/AC:L/AT:N/PR:H/UI:N/VC:H/VI:H/VA:H/SC:N/SI:N/SA:N/E:X/CR:X/IR:X/AR:X/MAV:X/MAC:X/MAT:X/MPR:X/MUI:X/MVC:X/MVI:X/MVA:X/MSC:X/MSI:X/MSA:X/S:X/AU:X/R:X/V:X/RE:X/U:X
    • Attack vector: Network
    • Attack complexity: Low
    • Attack requirements: None
    • Privileges required: High
    • User interaction: None
    • Vulnerable-system confidentiality: High
    • Vulnerable-system integrity: High
    • Vulnerable-system availability: High
    • Subsequent-system confidentiality: Negligible
    • Subsequent-system integrity: None
    • Subsequent-system availability: None
    • Safety: Not defined
  • CWE: CWE-73 — External Control of File Name or Path
  • Related CAPEC attack patterns (via MITRE CWE relationships): CAPEC-13 , CAPEC-267 , CAPEC-64 , CAPEC-72 , CAPEC-76 , CAPEC-78 , CAPEC-79 , CAPEC-80
  • Vendor: Plex
  • Vulnerable product: Media Server
  • CVE published: 2026-09-23
  • CVE last modified: 2026-10-21
  • Affected versions (NVD configurations):
    • media server: < 1.43.3.10861
  • EPSS: 0.0082; 56.7th percentile as of 2026-10-23 (FIRST )
  • CISA KEV: Listed (added 2026-10-20)
    • Known ransomware campaign use: Unknown
  • Latest Update: 2026-10-24
  • Reviewed Rule IDs: 398125
  • Reviewed rules with current blocking actions: 398125
  • Request surfaces inspected: JSON request data, Request arguments, SOAP request data
Technical vulnerability details · CVSS assessments, exploit evidence & CPE data

CVSS assessments

CVSS v4.0 · cisa-cg

  • Base score: 8.6
  • Base severity: HIGH
  • Assessment type: Secondary
  • Source identifier: 9119a7d8-5eab-497f-8521-727c672e3725
  • Full vector: CVSS:4.0/AV:N/AC:L/AT:N/PR:H/UI:N/VC:H/VI:H/VA:H/SC:N/SI:N/SA:N/E:X/CR:X/IR:X/AR:X/MAV:X/MAC:X/MAT:X/MPR:X/MUI:X/MVC:X/MVI:X/MVA:X/MSC:X/MSI:X/MSA:X/S:X/AU:X/R:X/V:X/RE:X/U:X
    • Attack vector: Network
    • Attack complexity: Low
    • Attack requirements: None
    • Privileges required: High
    • User interaction: None
    • Vulnerable-system confidentiality: High
    • Vulnerable-system integrity: High
    • Vulnerable-system availability: High
    • Subsequent-system confidentiality: Negligible
    • Subsequent-system integrity: None
    • Subsequent-system availability: None
    • Safety: Not defined
  • Exploit maturity: Not scored

CVSS v3.1 · cisa-cg

  • Base score: 7.2
  • Base severity: HIGH
  • Exploitability subscore: 1.2
  • Impact subscore: 5.9
  • Assessment type: Secondary
  • Source identifier: 9119a7d8-5eab-497f-8521-727c672e3725
  • Full vector: CVSS:3.1/AV:N/AC:L/PR:H/UI:N/S:U/C:H/I:H/A:H
    • Attack vector: Network
    • Attack complexity: Low
    • Privileges required: High
    • User interaction: None
    • Scope: Unchanged
    • Confidentiality impact: High
    • Integrity impact: High
    • Availability impact: High
  • Exploit maturity: Not scored

Exploitability and impact subscores describe the vulnerability’s technical characteristics. Exploit maturity describes the reported state of exploitation; these are separate measures.

Assessment source: NVD record · CVE record

CISA SSVC assessments

These are CISA’s published decision points at the assessment time. They are not a complete organization-specific prioritization decision.

  • Provider: CISA ADP

  • Provider identifier: 134c704f-9b21-4f2e-91b3-4a467353bcc0

  • SSVC version: 2.0.3

  • Role: CISA Coordinator

  • Assessment timestamp: 2026-10-20T19:46:34.862476Z

  • Exploitation: active

  • Automatable: no

  • Technical Impact: total

  • Source: CISA ADP in the CVE record

  • Provider: CISA ADP

  • Provider identifier: 134c704f-9b21-4f2e-91b3-4a467353bcc0

  • SSVC version: 2.0.3

  • Role: CISA Coordinator

  • Assessment timestamp: 2026-10-19T00:00:00+00:00

  • Exploitation: active

  • Automatable: no

  • Technical Impact: total

  • Source: CISA ADP in the CVE record

Vulnerable CPE configurations

  • cpe:2.3:a:plex:media_server:*:*:*:*:*:*:*:*
    • Version end (exclusive): 1.43.3.10861
    • NVD match criteria ID: 4C230270-5EBA-476B-84EE-59764545E0FD

Vulnerability Description

Plex Media Server before 1.43.3.10861 allows an admin user to write arbitrary files that may be executed on load. The preference TranscoderH264Options is appended verbatim to x264’s option string on every transcode. At startup, all .so files are run without signature, execute bit, or symbol checks.

  1. Maintain the reviewed Atomicorp rules. Keep your Atomicorp commercial rules current and confirm that the reviewed rules (398125 ) have not been locally disabled. Atomicorp commercial rules are enabled by default. If you use Atomic WAF, review the applicable policy and rule settings.

  2. Apply the vendor’s remediation. WAF protection is defense in depth and does not replace upgrading or following the affected vendor’s guidance.

    • Affected versions: Plex Media Server versions earlier than 1.43.3.10861.
    • Versions reported unaffected: Plex Media Server version 1.43.3.10861. Upgrade Plex Media Server to 1.43.3.10861 or a later supported release, following Plex’s security advisory and its platform-specific installation instructions. Confirm the running server version after the update and keep Atomicorp rules current.

    Plex reports active exploitation. Follow the advisory’s guidance for checking for compromise and recovering affected systems, including account security actions.

    • CISA KEV required action: Apply mitigations in accordance with vendor instructions, ensuring compliance with CISA’s BOD 26-04 Prioritizing Security Updates Based on Risk (see URL in Notes) guidance and CISA’s “Forensics Triage Requirements” (see URL in Notes). Follow applicable BOD 26-04 guidance for cloud services or discontinue use of the product if mitigations are unavailable. Stakeholders are responsible for evaluating each asset’s internet exposure and ensuring adherence to BOD 26-04 patching guidelines.
    • CISA KEV federal remediation due date: 2026-10-23

  3. Validate after changes. Confirm rule updates are current, review WAF events for the affected application, and test application behavior after vendor upgrades, mitigations, or local policy changes.

Research Notes

Atomicorp WAF protections are designed around attack techniques and exploit behaviors, allowing existing protections to apply across multiple vulnerabilities without requiring a unique rule for every CVE.

Public Vulnerability References

Test or Research Source

Research Note Context

This research note documents exploit-technique analysis associated with this vulnerability and references Atomicorp WAF protections observed during engineering review, testing, or validation activities.

Atomicorp security controls are generally designed to identify and mitigate attack techniques and exploit behaviors rather than individual CVE identifiers. As a result, protections developed for one vulnerability may also apply to related attack variants and future vulnerabilities using similar techniques.

Learn More

Atomicorp develops commercially supported security technologies for web applications, servers, endpoints, workloads, and legacy enterprise platforms.

Organizations interested in protecting systems against exploit techniques associated with vulnerabilities such as this one can learn more about:

  • Atomic ModSecurity Rules: commercially maintained WAF rules for ModSecurity deployments, including protections for web attacks, bots, scanners, malware, exploitation attempts, and emerging vulnerability classes.
  • Atomic WAF: an enterprise web application firewall with Atomicorp rules, centralized management, reporting, authentication controls, and operational tooling.
  • Atomic ModSecurity Integrator: a special licensing option for MSPs, MSSPs, OEMs, VARs, reverse proxy providers, and other integrators who want to incorporate Atomicorp ModSecurity rule technology into their own products or services.
  • Atomic OSSEC: an enterprise OSSEC-based intrusion detection, compliance, and security monitoring platform.
  • Atomic Protector: workload protection for Linux, web, cloud, data center, and hybrid environments.

For additional information, product evaluations, or technical discussions, visit https://www.atomicorp.com/ or https://modsecurity.io/ .