CVE-2026-40296 | PhpSpreadsheet vulnerable to XSS in HTML writer via custom number format codes

Exp

PhpSpreadsheet is a pure PHP library for reading and writing spreadsheet files. The HTML writer skips htmlspecialchars escaping when a cell's formatted value differs from the original value. When a cell has a custom number format containing the text placeholder @ along with any additional literal characters (for example ". @", "@ ", or "x@"), the formatter replaces @ with the cell value and adds the extra characters, causing the formatted value to differ from the original and bypassing HTML escaping entirely. An attacker who can control the cell value and number format of an uploaded spreadsheet that is later converted to HTML and displayed to other users can achieve stored cross-site scripting. This issue is fixed in versions 5.7.0, 3.10.5, 2.4.5, 2.1.16, and 1.30.4.

Published: 2026-05-06 Last update: 2026-05-11 Assigner: [email protected] Source: [email protected]
NVD Status：Analyzed，CVE State: published
View at NVD, CVE.org, EUVD

CVE-2026-40296 is rated Exploit Available (50/100): CVSS Medium severity, with low exploitation likelihood (EPSS 0.03%). 1 public exploit reference(s) are indexed (Exploit-DB). Public exploits are available—assess exposure, apply mitigations, and prioritize patching.

Risk is dynamic; we continuously reassess and refresh what is shown on this page as upstream context changes.

Public exploit references (Exploit-DB) for CVE-2026-40296

EDB-ID Source Kind Published Link
— nvd_ref exploit_tag Exploit-DB ↗

Exploit prediction scoring system (EPSS) score for CVE-2026-40296

EPSS lead: Daily EPSS estimates relative likelihood of exploitation; percentile ranks this CVE among scored vulnerabilities (higher = more severe relative rank).

# Date Old EPSS score New EPSS score Delta (New - Old)
1 2026-05-07 — 0.03% —

Full EPSS history (1 record total)

Common vulnerability scoring system (CVSS) metrics for CVE-2026-40296

CVSS metrics for this CVE.

Base score Version Severity Vector Exploitability Impact Score source
5.4 3.1 MEDIUM
CVSS:3.1/AV:N/AC:L/PR:L/UI:R/S:C/C:L/I:L/A:N Click to expand
Attack vector (AV:N)
Could be attacked over the internet or any normal routed network—not just someone sitting at the machine.
Attack complexity (AC:L)
Once they can reach the bug, pulling it off is straightforward—no weird race conditions or rare setup.
Privileges required (PR:L)
A normal user session is enough; they don’t have to be admin.
User interaction (UI:R)
A real person has to do something—click, install, enable—otherwise it doesn’t land.
Scope (S:C)
Breaking this can reach past the original component and bite other resources—bigger blast radius.
Confidentiality (C:L)
Some sensitive info could get out, but not a total data dump.
Integrity (I:L)
Attackers could change some data, but it’s limited—not everything goes.
Availability (A:N)
Service keeps running; no real outage angle.
 2.3 2.7 [email protected]

Weakness enumeration for CVE-2026-40296

GitHub Security Advisory for CVE-2026-40296

GHSA-hrmw-qprp-wgmc · Severity: medium · Ecosystem: composer — PhpSpreadsheet has XSS via number format code with @ text placeholder bypasses htmlspecialchars in HTML writer

Affected software / configurations for CVE-2026-40296

Vendor Product Version Raw CPE
phpoffice phpspreadsheet < 1.30.4 cpe:2.3:a:phpoffice:phpspreadsheet:*:*:*:*:*:*:*:*
phpoffice phpspreadsheet >= 2.0.0, < 2.1.16 cpe:2.3:a:phpoffice:phpspreadsheet:*:*:*:*:*:*:*:*
phpoffice phpspreadsheet >= 2.2.0, < 2.4.5 cpe:2.3:a:phpoffice:phpspreadsheet:*:*:*:*:*:*:*:*
phpoffice phpspreadsheet >= 3.3.0, < 3.10.5 cpe:2.3:a:phpoffice:phpspreadsheet:*:*:*:*:*:*:*:*
phpoffice phpspreadsheet >= 4.0.0, < 5.7.0 cpe:2.3:a:phpoffice:phpspreadsheet:*:*:*:*:*:*:*:*

References for CVE-2026-40296

cvelogic Threat Intelligence