---
title: "CVE-2026-33439: OpenIdentityPlatform OpenAM: Pre-Authentication Remote Code Execution via `jato.clientSession` Deserialization in OpenAM"
url: https://erroneo.us/security/cve/CVE-2026-33439/
description: "CVE-2026-33439 (org.openidentityplatform.openam:openam (Maven)): Open Access Management (OpenAM) is an access management solution. Prior to 16.0.6…"
type: vulnerability-record
section: "Security Digest"
date_published: 2026-04-07
date_modified: 2026-04-08
publisher: erroneo.us
author: erroneo.us Security Desk
cve: "CVE-2026-33439"
kev: false
cvss: 9.3
epss: 0.08428
license: All rights reserved. Quote with attribution and a link.
---

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

**Signal:** Critical and remotely reachable. No known exploitation yet, but it is network-reachable without credentials. (Computed from CISA KEV, EPSS and CVSS; not an editorial verdict.)

## Should you act?

- 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.

## Affected packages

- Maven `org.openidentityplatform.openam:openam` <= 16.0.5 → fixed: 16.0.6

## Affected products (CVE record)

- OpenIdentityPlatform OpenAM: < 16.0.6

## Severity

- GitHub_M CVSS 4.0: 9.3 `CVSS:4.0/AV:N/AC:L/AT:N/PR:N/UI:N/VC:H/VI:H/VA:H/SC:N/SI:N/SA:N`
- GitHub CVSS 4.0: 9.3 `CVSS:4.0/AV:N/AC:L/AT:N/PR:N/UI:N/VC:H/VI:H/VA:H/SC:N/SI:N/SA:N`

## Exploitation

- 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.

## Sources

- [GitHub Advisory GHSA-2cqq-rpvq-g5qj](https://github.com/advisories/GHSA-2cqq-rpvq-g5qj)
- [CVE.org record CVE-2026-33439](https://www.cve.org/CVERecord?id=CVE-2026-33439)
- [NVD entry CVE-2026-33439](https://nvd.nist.gov/vuln/detail/CVE-2026-33439)
- [github.com](https://github.com/OpenIdentityPlatform/OpenAM/security/advisories/GHSA-2cqq-rpvq-g5qj)
- [github.com](https://github.com/OpenIdentityPlatform/OpenAM/commit/014007c63cacc834cc795a89fac0e611aebc4a32)
- [github.com](https://github.com/OpenIdentityPlatform/OpenAM/releases/tag/16.0.6)

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Source page: https://erroneo.us/security/cve/CVE-2026-33439/ · Security Digest: https://erroneo.us/security/ · More: https://erroneo.us/llms.txt