# October CMS: PHP Object Injection via Backend Widget Session Storage

Advisory record · `GHSA-2ff2-mx52-q8wp`

- **Identifiers:** `GHSA-2ff2-mx52-q8wp` · `CVE-2026-49400` · `PKSA-syjw-hb9p-2d5m`
- **State:** Confirmed
- **Severity:** CVSS 3.3 Low
- **Critical:** No
- **Weakness (CWE):** [CWE-502](https://cwe.mitre.org/data/definitions/502.html)
- **Tags:** [Insecure deserialization](https://agentprime.io/advisories/tag/deserialization.md)
- **Published:** 14 Sept 2026
- **Updated:** 14 Sept 2026
- **Reviewed by a person:** No

Published by the GitHub Advisory Database at 14 Sept 2026, 17:08 UTC. agentprime has not analysed this yet, so whether it affects any app is not known.

## Affected packages

- `october/system` (Packagist): affected `<3.7.17 || >=4.0.0, <4.2.23`; fixed in `3.7.17`, `4.2.23`

## Machine-written summary

Summary written by Claude Haiku from the source advisory. Not reviewed by a person.

> October CMS's system package (october/system) versions below 3.7.17, and 4.0.0 through 4.2.22, deserialize widget session data without restricting which classes can be created. Only installations with \`cms.safe_mode\` enabled are affected. An attacker would need a backend account with CMS markup editing access and a usable PHP gadget chain in the installed dependencies to run arbitrary PHP code as the web server user. Upgrade to 3.7.17 or 4.2.23.

Written 31 Oct 2026.

## Not analysed yet

We haven’t published our analysis of this Advisory yet. Once a person has reviewed it, this page will say what’s vulnerable, what has to be true for your app to be affected, and how to check.

## Severity and exploitation

- 3.3 Low, CVSS 3.1: `CVSS:3.1/AV:N/AC:H/PR:H/UI:N/S:U/C:L/I:L/A:N`, from CNA (GitHub_M)

- **CISA KEV:** Not listed.
- **EPSS:** 0.0024, the 14th percentile, on 9 Nov 2026: FIRST’s estimate of the chance of exploitation in the next 30 days.

## Timeline

- 31 Oct 2026, 13:56 UTC: First seen by agentprime
- 31 Oct 2026, 13:56 UTC: [Confirmed by OSV](https://osv.dev/vulnerability/GHSA-2ff2-mx52-q8wp)

## Sources

- [GitHub Advisory Database: GHSA-2ff2-mx52-q8wp](https://github.com/advisories/GHSA-2ff2-mx52-q8wp)
- [OSV: GHSA-2ff2-mx52-q8wp](https://osv.dev/vulnerability/GHSA-2ff2-mx52-q8wp)
- <https://github.com/octobercms/october/security/advisories/GHSA-2ff2-mx52-q8wp>
- <https://github.com/octobercms/october>

Facts on this page come from the GitHub Advisory Database (CC-BY 4.0), OSV and the other sources listed, as published. We don’t reproduce full advisory descriptions, which can contain exploit code.

## Check whether this affects you

A Match means an installed version is in the affected range above. Most don’t affect the app; agentprime hasn’t analysed this one yet.

- With the agentprime MCP server (<https://api.agentprime.io/mcp>), ask your agent to check the project: `check_lockfile` sends a lockfile, `check_packages` a list of installed packages, and both return the Matches and the upgrades that clear them. `get_advisory` returns this record. Setup: <https://agentprime.io/mcp.md>
- In a browser: <https://agentprime.io/check/> reads your lockfile in the browser, never uploading it.
- Whether it touches your code, with file and line: the Claude Code plugin, <https://agentprime.io/plugin.md>
- As JSON: <https://api.agentprime.io/v1/advisories/GHSA-2ff2-mx52-q8wp>, or `POST https://api.agentprime.io/v1/match` with your packages (<https://agentprime.io/api.md>)

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The web page: <https://agentprime.io/advisories/GHSA-2ff2-mx52-q8wp/>. Everything for agents: <https://agentprime.io/llms.txt>.