CVE-2026-35453

Description

PhpSpreadsheet is a library for reading and writing spreadsheet files. In versions 1.30.3 and earlier, 2.0.0 through 2.1.15, 2.2.0 through 2.4.4, 3.3.0 through 3.10.4, and 4.0.0 through 5.6.0, the HTML Writer skips htmlspecialchars() output escaping when a cell uses a custom number format containing the @ text placeholder with additional literal text (e.g., @ "items"). The escaping is only applied when the formatted output strictly equals the original cell value. When the format code contains @ with quoted literal text, the formatter substitutes the raw cell value into the format string and returns early without invoking the escaping callback. An attacker who can control cell content in a spreadsheet processed by the HTML Writer can inject arbitrary HTML and JavaScript into the generated output. This issue has been fixed in versions 1.30.4, 2.1.16, 2.4.5, 3.10.5, and 5.7.0.

CVSS v3.1 Score

5.4

MEDIUM

CVSS:3.1/AV:N/AC:L/PR:L/UI:R/S:C/C:L/I:L/A:N

EPSS — Exploit Prediction

0.0001

Probability of exploitation

0.01%

Percentile rank

EPSS estimates the probability that this vulnerability will be exploited in the wild within the next 30 days. A higher score means more likely to be exploited.

Weakness Type (CWE)

CWE-79 Cross-site Scripting (XSS)

Affected Products

Vendor	Product	Versions
phpoffice	phpspreadsheet	< 1.30.4
phpoffice	phpspreadsheet	2.0.0 — 2.1.16
phpoffice	phpspreadsheet	2.2.0 — 2.4.5
phpoffice	phpspreadsheet	3.3.0 — 3.10.5
phpoffice	phpspreadsheet	4.0.0 — 5.7.0

References

Advisories & Patches

https://github.com/PHPOffice/PhpSpreadsheet/security/advisories/GHSA-6wpp-88cp-7q68 https://github.com/PHPOffice/PhpSpreadsheet/security/advisories/GHSA-6wpp-88cp-7q68

Exploits

https://github.com/PHPOffice/PhpSpreadsheet/security/advisories/GHSA-6wpp-88cp-7q68 https://github.com/PHPOffice/PhpSpreadsheet/security/advisories/GHSA-6wpp-88cp-7q68

Frequently Asked Questions

What is CVE-2026-35453? +

PhpSpreadsheet is a library for reading and writing spreadsheet files. In versions 1.30.3 and earlier, 2.0.0 through 2.1.15, 2.2.0 through 2.4.4, 3.3.0 through 3.10.4, and 4.0.0 through 5.6.0, the HTML Writer skips htmlspecialchars() output escaping when a cell uses a custom number format containing the @ text placeholder with additional literal text (e.g., @ "items"). The escaping is only applied when the formatted output strictly equals the original cell value. When the format code contains @ with quoted literal text, the formatter substitutes the raw cell value into the format string and returns early without invoking the escaping callback. An attacker who can control cell content in a spreadsheet processed by the HTML Writer can inject arbitrary HTML and JavaScript into the generated output. This issue has been fixed in versions 1.30.4, 2.1.16, 2.4.5, 3.10.5, and 5.7.0. It has a CVSS v3.1 base score of 5.4 (MEDIUM).

How severe is CVE-2026-35453? +

CVE-2026-35453 has a CVSS v3.1 score of 5.4 out of 10, rated MEDIUM. This is a medium-severity vulnerability that should be remediated as part of regular maintenance. The EPSS score is 0.0001, placing it in the 0th percentile for exploitation probability.

What products are affected by CVE-2026-35453? +

CVE-2026-35453 affects products from phpoffice, specifically: phpspreadsheet. Check the affected products table above for specific version ranges.

How do I check if I'm vulnerable to CVE-2026-35453? +

You can use Secably's free Website Scanner to check your website for known vulnerabilities. For infrastructure scanning, use the Port Scanner to identify exposed services that may be affected. Check the vendor advisories linked above for specific patch and version information.

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