OpenAM: Pre-auth Reflected XSS in OAuth2 / OIDC response_mode=form_post via state parameter (FormPostResponse.ftl)

CVE Details

• Protection status: Protected by Atomicorp rules · About protection statuses
• CVE: CVE-2026-44203
• Name: OpenAM: Pre-auth Reflected XSS in OAuth2 / OIDC response_mode=form_post via state parameter (FormPostResponse.ftl)
• Severity: High
• CVSS: 8.3 (v4.0) (High)
• CVSS version: 4.0
• CVSS source: GitHub_M CNA
• CVSS vector: CVSS:4.0/AV:N/AC:L/AT:N/PR:N/UI:A/VC:L/VI:H/VA:N/SC:L/SI:H/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: None
  • User interaction: Active
  • Vulnerable-system confidentiality: Low
  • Vulnerable-system integrity: High
  • Vulnerable-system availability: None
  • Subsequent-system confidentiality: Low
  • Subsequent-system integrity: High
  • Subsequent-system availability: None
  • Safety: Not defined
• CWE: CWE-79
• Vendor: OpenIdentityPlatform
• Vulnerable product: OpenAM
• CVE published: 2026-09-15
• CVE last modified: 2026-09-15
• EPSS: 0.0047; 39.3th percentile as of 2026-09-16 (FIRST (opens in a new tab) )
• Latest Update: 2026-09-16
• Selected Rule IDs observed: 333140 , 333141 , 340087 , 340095 , 340099 , 340147 , 340148 , 341099 , 341256 , 341266 , 342259 , 346755 , 350147 , 350148
• Matching rules: 14; rules with blocking actions: 14
• Would-block Rule IDs: 333140 , 333141 , 340087 , 340095 , 340099 , 340147 , 340148 , 341099 , 341256 , 341266 , 342259 , 346755 , 350147 , 350148
• Request surfaces inspected: JSON request data, Request URI, Request argument names, Request arguments, Request cookies, Request filename, Request headers, SOAP request data, XML request data

Vulnerability Description

Open Access Management (OpenAM) is an access management solution. Prior to 16.1.1, the OAuth 2.0 and OpenID Connect authorization endpoint does not sufficiently encode user-supplied parameters before FormPostResponse.ftl and checkSession.ftl render them into HTML for the form_post response mode. An unauthenticated attacker can induce a user to open a crafted authorization request and execute script in the OpenAM origin. This issue is fixed in version 16.1.1.

Recommended Actions

1. Maintain the observed Atomicorp protections. Keep your Atomicorp commercial rules current and confirm that the selected observed rules (333140 , 333141 , 340087 , 340095 , 340099 , 340147 , 340148 , 341099 , 341256 , 341266 , 342259 , 346755 , 350147 , 350148 ) 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: OpenIdentityPlatform OpenAM version < 16.1.1.
   • No specific CNA/vendor solution or workaround is included in the current CVE Record (opens in a new tab) . Review the vendor’s security advisories and supported-release guidance before making changes.

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

• NVD (opens in a new tab)
• CVE Record (opens in a new tab)
• CVE authority reference: https://github.com/OpenIdentityPlatform/OpenAM/commit/078bd4754905f5130eaa7bbe45f958eaeb7fd0d7 (opens in a new tab)
• CVE authority reference: https://github.com/OpenIdentityPlatform/OpenAM/releases/tag/16.1.1 (opens in a new tab)
• CVE authority reference: https://github.com/OpenIdentityPlatform/OpenAM/security/advisories/GHSA-fq9h-c788-fx73 (opens in a new tab)

Test or Research Source

• Source: Atomicorp AI Research Framework
• Tags: cve, derived, waf-probe, xss

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/ (opens in a new tab) .