CVE-2026-34084
Published: 05 May 2026
Summary
CVE-2026-34084 is a critical-severity Deserialization of Untrusted Data (CWE-502) vulnerability in Phpoffice Phpspreadsheet. Its CVSS base score is 9.8 (Critical).
Operationally, ranked at the 31.4th percentile by exploit likelihood (below the median); it is not currently listed in the CISA KEV catalog; a public proof-of-concept is referenced.
Threat & Defense Details
Likely Mitigating ControlsAI
Per-CVE control mapping for this CVE has not run yet; the list below is derived from the weakness types (CWEs) cited in the NVD entry.
Penetration testing attempts server-side requests to internal resources, identifying SSRF weaknesses for remediation.
Validates server-side URLs and resource references to block SSRF attempts.
Evaluation of untrusted data handling (deserialization testing) reveals unsafe processing, which the required remediation process addresses.
Untrusted serialized data can be deserialized and observed inside the chamber, blocking gadget-chain exploitation outside the sandbox.
Outbound connections to external resources can be monitored and limited at the boundary, reducing SSRF impact.
Identifies and blocks malicious code introduced through deserialization of untrusted data at system boundaries.
Detects server-side request forgery through monitoring of unexpected outbound connections.
Integrity verification of serialized information can detect tampering before deserialization occurs.
NVD Description
PhpSpreadsheet is a library for reading and writing spreadsheet files. In versions 1.30.2 and earlier, 2.0.0 through 2.1.14, 2.2.0 through 2.4.3, 3.3.0 through 3.10.3, and 4.0.0 through 5.5.0, when the filename argument to IOFactory::load() is user-controlled, an attacker can supply…
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a PHP stream wrapper path (such as phar://, ftp://, or ssh2.sftp://) that passes the is_file() check in File::assertFile(). The phar:// wrapper triggers deserialization of the PHAR metadata, which can lead to remote code execution if a suitable gadget chain is available in the application. The ftp:// and ssh2.sftp:// wrappers can be used for server-side request forgery. This issue has been fixed in versions 1.30.3, 2.1.15, 2.4.4, 3.10.4, and 5.6.0.
Deeper analysisAI
Automated synthesis unavailable for this CVE.
Details
- CWE(s)