CVE-2026-33439: OpenIdentityPlatform OpenAM: Pre-Authentication Remote Code Execution via `jato.clientSession` Deserialization in OpenAM

Should you act?

Critical and remotely reachable

No known exploitation yet, but it is network-reachable without credentials. This signal is computed from CISA KEV, EPSS and CVSS data; it is not an editorial verdict.

• No confirmed exploitation. It is not in CISA’s KEV catalog and CISA’s SSVC assessment records no known exploitation. That can change quickly after a public write-up; re-check if you are affected.
• EPSS 8.4%, percentile 95: FIRST’s model estimates a 8.4% chance of exploitation activity in the next 30 days, higher than 95% of all scored CVEs (elevated). EPSS is a probability, not a verdict.
• Remotely reachable with no login and no user interaction. If the vulnerable service is exposed to the internet, prioritize it.
• Only applies if your dependency tree includes org.openidentityplatform.openam:openam (Maven) <= 16.0.5, fixed in 16.0.6. Check your lockfile, including transitive dependencies.

What it is

Open Access Management (OpenAM) is an access management solution. Prior to 16.0.6, OpenIdentityPlatform OpenAM is vulnerable to pre-authentication Remote Code Execution (RCE) via unsafe Java deserialization of the jato.clientSession HTTP parameter. This bypasses the WhitelistObjectInputStream mitigation that was applied to the jato.pageSession parameter after CVE-2021-35464. An unauthenticated attacker can achieve arbitrary command execution on the server by sending a crafted serialized Java object as the jato.clientSession GET/POST parameter to any JATO ViewBean endpoint whose JSP contains tags (e.g., the Password Reset pages). This vulnerability is fixed in 16.0.6.

From the GitHub advisory

Summary

OpenIdentityPlatform OpenAM 16.0.5 (and likely earlier versions) is vulnerable to pre-authentication Remote Code Execution (RCE) via unsafe Java deserialization of the jato.clientSession HTTP parameter. This bypasses the WhitelistObjectInputStream mitigation that was applied to the jato.pageSession parameter after CVE-2021-35464.

An unauthenticated attacker can achieve arbitrary command execution on the server by sending a crafted serialized Java object as the jato.clientSession GET/POST parameter to any JATO ViewBean endpoint whose JSP contains tags (e.g., the Password Reset pages).

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Vulnerability Details

Weakness type: CWE-502.

Product: org.openidentityplatform.openam:openam (Maven) · Assigned by: GitHub_M · Published: 2026-04-07

Affected and fixed versions

Severity scores

• Attack vector: network (remotely reachable)
• Attack complexity: low
• Attack requirements: none
• Privileges required: none (no login)
• User interaction: none

CVSS measures how bad a flaw is if exploited, not how likely exploitation is. Read it next to the exploitation data below.

Exploitation and urgency

• CISA KEV: not listed (no confirmed in-the-wild exploitation known to CISA).
• CISA SSVC assessment: exploitation none, automatable yes, technical impact total.
• FIRST EPSS (model of 2026-10-21): 8.43% probability of exploitation activity in the next 30 days; percentile 95.

Timeline

• 2026-04-07 — CVE record published by GitHub_M
• 2026-04-07 — GitHub-reviewed advisory GHSA-2cqq-rpvq-g5qj published (critical)
• 2026-04-08 — CVE record last updated

Sources and references

Original sources first. Version and fix details should always be confirmed against the vendor or project advisory.

Vulnerability records

1. GitHub Advisory GHSA-2cqq-rpvq-g5qj github.com
2. CVE.org record CVE-2026-33439 cve.org
3. NVD entry CVE-2026-33439 nvd.nist.gov

Other references from the CVE record and advisory

1. github.com github.com
2. github.com github.com
3. github.com github.com

Critical Maven advisories · Today’s Security Digest