Cross-Site Scripting (XSS) in phpoffice/phpspreadsheet (CVE-2026-35453)
Summary
Cross-site scripting in phpoffice/phpspreadsheet (CVE-2026-35453). Risk of unauthorized operations or information disclosure. Exploitable via formatColor. Mitigation: upgrade to 1.30.4 or later.
Original description
The description as published by the source.
Summary
The HTML Writer in PhpSpreadsheet bypasses htmlspecialchars() output escaping when a cell uses a custom number format containing the @ text placeholder with additional literal text (e.g., @ "items" or "Total: "@). This allows an attacker to inject arbitrary HTML and JavaScript into the generated HTML output by crafting a malicious XLSX file.
Details
1. Conditional escaping in Html.php:1586-1594
$cellData = NumberFormat::toFormattedString(
$origData2,
$formatCode ?? NumberFormat::FORMAT_GENERAL,
[$this, 'formatColor']
);
if ($cellData === $origData) {
$cellData = htmlspecialchars($cellData, Settings::htmlEntityFlags());
}
htmlspecialchars() is only called when $cellData === $origData (strict comparison). If the formatted output differs from the original value in any way, escaping is skipped entirely.
2. Early return in Formatter.php:136-152
if (preg_match(self::SECTION_SPLIT, $format) === 0
&& preg_match(self::SYMBOL_AT, $formatx) === 1) {
if (!str_contains($format, '"')) {
return str_replace('@', /* raw value */, $format);
}
return str_replace(/* ... preg_replace with raw value ... */);
}
When the format code contains @ with additional literal text (e.g., @ "items"), the formatter substitutes the raw cell value into the format string and returns early — the formatColor callback (which would have applied htmlspecialchars) is never invoked.
PoC
**tes…
Source: NIST National Vulnerability Database NVD GitHub Advisory
Auto-generated summary
Assembled by SecPulse from the source data (CVSS, CWE, affected versions) using templates — no AI involved. Check the original description and references below for exact details.
A vulnerability tracked as CVE-2026-35453 has been found in phpoffice/phpspreadsheet.
Attackers can target a specific entry point like formatColor over the network to misuse the product.
Risk of unauthorized operations or information disclosure. CVSS score: 5.4/10.
What to do: upgrade phpoffice/phpspreadsheet to 1.30.4 or later.
If unsure, ask your IT team or search "phpoffice/phpspreadsheet CVE-2026-35453" on the vendor's site.
CVE-2026-35453 (phpoffice/phpspreadsheet) — CWE-79 / CVSS v3 5.4
Attack vector: remote (network-reachable)
Attack surface: formatColor / htmlspecialchars
Patched: 1.30.4 — apply immediately
Plan: 1) Audit SBOM/dependencies, 2) Stage→prod upgrade, 3) Add WAF/proxy monitoring on affected endpoints, 4) Hunt IOCs in logs.
Refs: see the GHSA / vendor advisory / patched release linked on this page.
Cross-site scripting (XSS) (CWE-79) exists in phpoffice/phpspreadsheet. Attackers reach the vulnerable code path via formatColor.
Check the vendor advisory for the affected versions of phpoffice/phpspreadsheet. Attack surface: formatColor / htmlspecialchars.
Severity: Medium (CVSS 5.4/10). Risk of unauthorized operations or information disclosure.
Update to 1.30.4.
Until the patch is applied: disable the affected feature, apply WAF rules, or restrict access via network ACLs.
Search webserver/proxy logs for unusual request patterns matching this CVE's known IOCs. Run grep -r 'phpoffice/phpspreadsheet' . against your dependency files (package-lock.json, requirements.txt, go.sum) to find affected services.
Response actions
Concrete steps and command examples for SOC/SRE teams to execute in order
-
1Identify exposure identify
grep -r 'phpoffice/phpspreadsheet' . | grep -v node_modulesリポジトリと本番環境の依存ファイル (package-lock.json / requirements.txt / go.sum / Gemfile.lock 等) で
phpoffice/phpspreadsheetを grep し、稼働しているサービス・バージョンを把握する。 -
2Apply patch patch
Upgrade phpoffice/phpspreadsheet to 1.30.4ステージング環境で 1.30.4 に上げて回帰テスト → 本番反映。回帰テストはアプリの主要ハッピーパスを含めること。
-
3Post-deployment verification verify
Confirm patched version is live in productionパッチ適用後、ステージングで PoC または同等の悪用パターンを再現して脆弱性が閉じたことを確認。本番ではアクセスログ・WAF でアラート再発が無いか継続監視。
Affected packages
References
- advisory nvd.nist.gov
- exploit github.com
- package github.com
- web github.com