Security readout for executives and security teams
Plain-English summary
CVE-2026-0859 is a TYPO3 CMS flaw where a user who can write files into the mail spool can trigger unsafe PHP object deserialization when mailer:spool:send runs. Successful exploitation can execute PHP code on the server. It is not described as remotely exploitable without prior local/write access.
Executive priority
Treat as a priority for TYPO3 environments with shared hosting, many local users, or complex extensions. The issue can lead to server-side code execution, but the required local/write access keeps urgency below internet-facing remote-code-execution cases.
Technical view
TYPO3 CMS mail-file spool handling deserializes attacker-controlled spool files during the mailer:spool:send command. The issue is CWE-502 insecure deserialization and affects typo3/cms-core versions 10.0.0-10.4.54, 11.0.0-11.5.48, 12.0.0-12.4.40, 13.0.0-13.4.22, and 14.0.0-14.0.1.
Likely exposure
Exposure is most relevant where TYPO3 uses file-based mail spooling and local users, compromised accounts, extensions, or processes can write to the spool directory. Internet exposure alone is not enough based on the provided sources.
Exploitation context
The CVSS vector requires local access, low privileges, and a precondition: write access to the spool directory. No source in the bundle indicates active exploitation, and the CVE is not listed as KEV.
Researcher notes
Key unknowns from the provided bundle: exact fixed version numbers and any public exploitation evidence. Analysis should focus on TYPO3 mail spool configuration, filesystem permissions, and whether untrusted principals can place files in the spool directory.
Mitigation direction
- Review TYPO3 advisory TYPO3-CORE-SA-2026-004 for fixed release guidance.
- Update affected TYPO3 CMS installations to a vendor-supported non-affected version.
- Apply the referenced TYPO3 core patches if maintaining custom builds.
- Restrict write permissions on the mail spool directory to required trusted processes only.
- Review local accounts, deployment users, and extensions with filesystem write access.
Validation and detection
- Inventory TYPO3 CMS versions and compare against the affected ranges.
- Confirm whether file-based mail spooling is enabled or used.
- Check spool directory ownership and write permissions.
- Verify vendor patch or fixed release is applied.
- Review recent spool files and server logs for suspicious local write activity.
Public sources used
Generated from the cited source records. This long-tail analysis has not been individually reviewed by a named human.
Conservative CVE-to-ATT&CK context
These mappings and lookup hints may be relevant to the vulnerability behavior, CWE, affected product, or exposure path. Glexia-inferred context is not an official MITRE, ATT&CK, CWE, or CVE Program mapping.
ATT&CK lookup starting points
Use these exact CWE pages and searches to review the Glexia ATT&CK library from this CVE's weakness and description context.
CWE-502: Code execution behavior lookup
Code execution and unsafe deserialization weaknesses often justify reviewing execution behavior and process telemetry. Open the exact CWE lookup page first, then review the ATT&CK searches from that MITRE weakness context. This is a Glexia lookup hint, not an official ATT&CK mapping.
Open ATT&CK lookupExecution behavior lookup
The CVE wording references code or command execution, so execution technique review may help defensive triage. This is a Glexia inferred lookup path, not an official MITRE, ATT&CK, or CVE Program mapping.
Open ATT&CK lookupCVE-2026-0859 mapping review
Open the CVE-to-ATT&CK bridge for reviewed, inferred, or future official mappings tied to this CVE.
Open ATT&CK lookup- Severity
- Medium
- CVSS
- 5.2 (4.0)
- Known Exploited
- No
- Published
Vector: CVSS:4.0/AV:L/AC:L/AT:P/PR:L/UI:N/VC:N/VI:L/VA:N/SC:H/SI:H/SA:H
CNA and ADP enrichment extracted from CVE v5
These fields come from the CVE record and ADP containers, not from Glexia's Take. They preserve time-varying source decisions such as CISA SSVC, KEV status, CVSS metrics, and provider references.
CVSS vector scores
1 official scoreWe collect every scored CVSS vector available in the official CNA and ADP containers. When more than one version is present, the table keeps the source vectors side by side instead of collapsing them into the highest score.
CVSS:4.0/AV:L/AC:L/AT:P/PR:L/UI:N/VC:N/VI:L/VA:N/SC:H/SI:H/SA:H——Primary CVE scoreVulnerability scoring details
Base CVSS 4.0 score
5.2MediumVector: CVSS:4.0/AV:L/AC:L/AT:P/PR:L/UI:N/VC:N/VI:L/VA:N/SC:H/SI:H/SA:H
Source materials
- CVE List V5 sourceCVE List V5
- https://typo3.org/security/advisory/typo3-core-sa-2026-004CVE reference · vendor-advisory
- Git commit of main branchCVE reference · patch
- Git commit of 13.4 branchCVE reference · patch
- Git commit of 12.4 branchCVE reference · patch
Products and packages named in the record
CWE details
CWE links open Glexia weakness intelligence pages with official CWE context, developer remediation guidance, and related CVE mappings.
Deserialization of Untrusted Data
Deserialization of Untrusted Data represents a recurring weakness pattern that can create exploitable paths when design, validation, or implementation controls are missing.