CVE-2026-45034: PHPSpreadsheet has a patch bypass for CVE-2026-34084

Should you act?

Critical and remotely reachable

No known exploitation yet, but it is network-reachable without credentials. This signal is computed from CISA KEV, EPSS and CVSS data; it is not an editorial verdict.

• Not in CISA KEV, but CISA’s SSVC assessment records a public proof-of-concept, so attack code exists.
• EPSS 0.5%, percentile 39: FIRST’s model estimates a 0.5% chance of exploitation activity in the next 30 days, higher than 39% of all scored CVEs (low). 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 phpoffice/phpspreadsheet (Composer (PHP)) <= 1.30.4, fixed in 1.30.5. Check your lockfile, including transitive dependencies.

What it is

PhpSpreadsheet is a pure PHP library for reading and writing spreadsheet files. Prior to 1.30.5, CVE-2026-34084 was patched by the helper File::prohibitWrappers. The helper calls parseurl($filename, PHPURLSCHEME) and then checks isstring($scheme) && strlen($scheme) > 1 to reject stream wrappers such as phar://, php://, data:// or expect://. The check is not equivalent to "does the path contain a wrapper". When the input has the form phar:///path/file.phar/inner with three or more slashes after the scheme, parseurl returns boolean false instead of returning the scheme string. The isstring($scheme) branch is therefore skipped, the helper returns without throwing, and the caller proceeds. PHP's stream layer, however, still treats phar:///... as a valid phar wrapper and opens the underlying phar file. The result is that IOFactory::load($attackerPath) walks past the patch and still touches the phar wrapper. On PHP 7.x, simply reaching the phar wrapper via isfile is enough for PHP to automatically deserialize the phar metadata, which in turn invokes the magic methods wakeup and destruct of an attacker controlled object and gives full RCE. On PHP 8.x, automatic metadata deserialization for plain file ops was removed, so the chain at the PhpSpreadsheet layer reduces to a phar wrapper file read primitive, and RCE only resurfaces if the downstream consumer ever calls Phar::getMetadata. This vulnerability is fixed in 1.30.5.

From the GitHub advisory

Summary

CVE-2026-34084 was patched by the helper File::prohibitWrappers. The helper calls parseurl($filename, PHPURLSCHEME) and then checks isstring($scheme) && strlen($scheme) > 1 to reject stream wrappers such as phar://, php://, data:// or expect://. The check is not equivalent to "does the path contain a wrapper". When the input has the form phar:///path/file.phar/inner with three or more slashes after the scheme, parseurl returns boolean false instead of returning the scheme string. The isstring($scheme) branch is therefore skipped, the helper returns without throwing, and the caller proceeds. PHP's stream layer, however, still treats phar:///... as a valid phar wrapper and opens the underlying phar file. The result is that IOFactory::load($attackerPath) walks past the patch and still touches the phar wrapper. On PHP 7.x, simply reaching the phar wrapper via isfile is enough for PHP to automatically deserialize the phar metadata, which in turn invokes the magic methods wakeup and destruct of an attacker controlled object and gives full RCE. On PHP 8.x, automatic metadata deserialization for plain file ops was removed, so the chain at the PhpSpreadsheet layer reduces to a phar wrapper file read primitive, and RCE only resurfaces if the downstream consumer ever calls Phar::getMetadata.

Vulnerable code

The file vendor/phpoffice/phpspreadsheet/src/PhpSpreadsheet/Shared/File.php is byte identical across all six latest tags listed below:

For input phar://x/dummy.csv the call returns the string "phar" and the throw fires correctly. For input phar:///work/exploit.phar/dummy.csv the same call returns false and the throw is skipped, which is the bypass.

Weakness type: CWE-502.

Product: phpoffice/phpspreadsheet (Composer (PHP)) · Assigned by: GitHub_M · Published: 2026-06-22

Affected and fixed versions

Severity scores

• Attack vector: network (remotely reachable)
• Attack complexity: low
• Attack requirements: present (depends on deployment conditions)
• Privileges required: none (no login)
• User interaction: none

CVSS measures how bad a flaw is if exploited, not how likely exploitation is. Read it next to the exploitation data below.

Exploitation and urgency

• CISA KEV: not listed (no confirmed in-the-wild exploitation known to CISA).
• CISA SSVC assessment: exploitation poc, automatable yes, technical impact total.
• FIRST EPSS (model of 2026-10-21): 0.46% probability of exploitation activity in the next 30 days; percentile 39.

Timeline

• 2026-06-08 — GitHub-reviewed advisory GHSA-87m4-826x-3crx published (critical)
• 2026-06-22 — CVE record published by GitHub_M
• 2026-06-23 — CVE record last updated

Sources and references

Original sources first. Version and fix details should always be confirmed against the vendor or project advisory.

Vulnerability records

1. GitHub Advisory GHSA-87m4-826x-3crx github.com
2. CVE.org record CVE-2026-45034 cve.org
3. NVD entry CVE-2026-45034 nvd.nist.gov

Other references from the CVE record and advisory

1. github.com github.com
2. github.com github.com

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