CVE-2026-49400 — October CMS: PHP Object Injection via Backend Widget Session Storage
October System provides the system module for October Content Management System. Prior to versions 3.7.17 and 4.2.21, the backend `SessionMaker` trait stored widget session state as `base64(serialize(...))` and consumed it with `unserialize()` without an `allowed_classes` restriction. Any code path that could write to a `widget.*` session key with attacker-controlled bytes could trigger PHP object injection the next time the widget read its session state, allowing instantiation of arbitrary classes and reachable PHP gadget chains. This issue only affects installations running with `cms.safe_mode` enabled. Safe Mode is a niche opt-in feature, primarily used for demo installations and multi-tenant or shared-editor scenarios where untrusted users are deliberately granted access to the CMS markup editor. In standard production deployments Safe Mode is off, backend access is restricted to trusted administrators, and a markup editor can already execute arbitrary PHP directly. The session-write path that reaches this sink is gated by the Safe Mode sandbox, so installations without Safe Mode enabled are not exposed. Scope of impact is narrow even with Safe Mode enabled. The standard backend code paths that populate widget session state (search terms, sort options, selected IDs, filter values) wrap the input inside a known array shape before serializing, so user-supplied values never reach `unserialize()` as a controllable serialized payload. Exploitation requires the Safe Mode session-write path together with a suitable PHP gadget chain reachable from the installed dependency set. The hardening below removes the underlying object-injection sink so the class of issue is closed off regardless. The vulnerability has been patched in v3.7.17 and v4.2.21. Two changes were applied. `Backend\Traits\SessionMaker` now stores widget session state as plain JSON instead of `base64(serialize(...))`, eliminating the object-injection sink entirely for new writes. Reads transparently fall back to the legacy format for one upgrade cycle so existing sessions retain their saved widget state. The legacy `unserialize()` fallback path now sets `allowed_classes => false`, so even values written before the upgrade cannot instantiate objects. As a workaround, restrict CMS markup editing access to fully trusted administrators only, the standard October CMS recommendation for any deployment.
Who exploits it and how urgent it is
A 0–100 score combining confirmed exploitation, ransomware and APT use, public exploits, EPSS and severity.
How the score was calculated
- EPSS 0.2% (30-day exploitation probability)+2
The score orders the patch queue; it does not replace your asset context (internet exposure, criticality, compensating controls).
Triage
Is it exploited, how likely is exploitation, what does it touch, and how severe do the sources call it.
CISA SSVC assessment CISA
Three decision points CISA publishes for the CVEs it assesses (SSVC 2.0.3). A stakeholder decision, not a severity score.
Remediation
Fixes and mitigations documented by the sources — linked to the original advisory.
No fix documented by the sources we poll. That does not mean none exists: check the vendor advisory.
First 24 hours
Ordered from the record’s own fields — exposure first, because you cannot patch what you have not found. A rule-generated starting point.
- Identify exposed assets running the affected vendor/product/version combinations (Octobercms October).
- No fix documented in the sources: reduce exposure and monitor the vendor advisory.
- Search available logs for exploit probes matching the vulnerability class (insecure deserialization), errors and authentication anomalies.
Affected scope
Vendor, product and versions as the sources word them.
| Vendor | Product | Versions | Status | Source |
|---|---|---|---|---|
| Octobercms | October | version < 3.7.17version >= 4.0.0, < 4.2.23 | Vulnerable | CVE Program (cve.org) e CISA ADP |
Attack characteristics
The CVSS vector, decoded. It describes the attack, not your exposure to it.
Every base score collected
Sources score independently and may disagree; each row says who scored it and under which version.
| Score | Version | Severity | Expl. | Impact | Scored by |
|---|---|---|---|---|---|
| 3.3 | CVSS 3.1 | Low | 0.7 | 2.5 | security-advisories@github.com via NIST National Vulnerability Database |
| 3.3 | CVSS 3.1 | Low | — | — | GitHub_M via CVE Program (cve.org) e CISA ADP |
CVSS:3.1/AV:N/AC:H/PR:H/UI:N/S:U/C:L/I:L/A:N (score shown at the top: security-advisories@github.com) Weakness MITRE
Weakness class according to MITRE’s CWE catalog.
EPSS over time FIRST
Oct 15, 2026 → Oct 16, 2026 · 2 reading(s) · max 0.24%
Detection
Read off the CVSS vector and the weakness class. Starting points, not tested rules.
- Prioritize edge telemetry for the network-reachable component (proxy, WAF, IDS/IPS).
- Monitor serialized objects in requests and unexpected processes spawned by the runtime.
Timeline
What happened to this CVE, newest first.
- 2026
- Affected products added · octobercms/october
- SSVC assessment updated
- Record published
- CVSS changed · 3.3
- Source status changed · → Deferred
- Record created in this database
- CVE published
Source activity
Repeated readings are counted rather than listed.
- 1× Official description updated · Oct 15, 2026 – Oct 15, 2026
References
1 on the record
Elsewhere on this site
Related CVEs (same products)
- Low CVE-2026-29179 October: Editor Sub-Permission Bypass for Asset and Blueprint File Operations Apr 21, 2026
- Low CVE-2026-27937 October: Reflected XSS via DataTable Form Widget Apr 21, 2026
- Medium CVE-2026-26274 October: Safe Mode Bypass via Twig Database Write Operations Apr 21, 2026
- Medium CVE-2026-26067 October: Safe Mode Bypass via CSS Preprocessor Compilers Apr 21, 2026
- Medium CVE-2026-25125 October CMS: Environment Variable Exfiltration via INI Parser Interpolation Apr 14, 2026
- Medium CVE-2026-25133 October CMS has Stored XSS via SVG Filter Bypass Apr 14, 2026
Not in any source we poll
Listed rather than left blank: an empty field and an unmeasured one look identical on screen, and only one is a reason to look elsewhere.
- No fixed version, patch or mitigation documented.
- No confirmed IOCs, IP addresses, domains, file hashes, or malware artifacts supplied.
- No organization-specific asset inventory, compensating-control status, or patch deployment evidence supplied.
- No exploit packet captures, log samples, or incident case IDs supplied.
Answered from this record
Text assembled only from the fields above — no additional claims.
What should defenders know first?
CVE-2026-49400 is "October CMS: PHP Object Injection via Backend Widget Session Storage", rated Low. It affects October (Octobercms); versions are in the scope table. It is not in CISA KEV, which does not rule out exploitation. CVSS 3.3 describes technical severity. EPSS 0.24% estimates the probability of exploitation in 30 days; neither replaces your asset context. First verify whether exposed or business-critical assets run the affected versions, apply vendor fixes or mitigations, and preserve logs for review.
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