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CVE-2026-17545: On Windows, PHP's filesystem and stream APIs do not reject reserved device names such as CON, PRN, AUX, NUL, C

42
This week
HIGH 7.5REMOTEUPGRADE

CVE-2026-17545 is a high-severity flaw (CVSS 7.5) affecting php. Below: why it ranks where it does, which versions are affected, what to do, and the exact commands.

On Windows, PHP's filesystem and stream APIs do not reject reserved device names such as CON, PRN, AUX, NUL, COM1 to COM9, LPT1 to LPT9, CONIN$ and CONOUT$ when they appear as a component of a path. An attacker-controlled filename therefore reaches CreateFileW() and opens a device instead of the regular file the application expected, which can block or hang the request and exhaust worker processes.

Why this priority

  • High severity
  • Public exploit reference
  • Remotely exploitable, no login, no user action

A fixed release or distro patch exists.

Risk facts

CVSS score7.5 (High)
Attack vectorNetwork (remote)
Attack complexityLow
Privileges neededNone
User interactionNone
EPSS exploit chance0.3% (top 76%)
CISA exploited listNo
WeaknessCWE-67
Published2026-09-25
Last modified2026-10-23
Publisher (CNA): PHP Group · Vendor: php

Am I affected?

Timeline

php php UPGRADE
Affected: >= 8.2.0 and < 8.2.34 · >= 8.3.0 and < 8.3.35 · >= 8.4.0 and < 8.4.26 · >= 8.5.0 and < 8.5.11
Fixed in: 8.2.34, 8.3.35, 8.4.26, 8.5.11
Safe to downgrade to: a release before 8.2.0
1. Check installed version
apt-cache policy php || rpm -q php || php --version
2. UPGRADE to 8.2.34 (Debian / Ubuntu)
sudo apt update && sudo apt install --only-upgrade php
2. UPGRADE (RHEL / Amazon Linux / Fedora)
sudo dnf upgrade php
Note
Distros often backport fixes without changing the version number. Confirm with the distro advisory or changelog.
3. If no update is available yet, DOWNGRADE to a release before 8.2.0 (Debian / Ubuntu)
apt-cache madison php sudo apt install php=<VERSION_BEFORE_8.2.0> sudo apt-mark hold php
3. If no update is available yet, DOWNGRADE (RHEL / Amazon Linux / Fedora)
dnf --showduplicates list php sudo dnf downgrade php-<VERSION_BEFORE_8.2.0> sudo dnf versionlock add php
Downgrade risk
Downgrading can break dependent software and may reopen older bugs. Read the distro advisory first and test on a non-production host.
After downgrade
Restart the service, and keep the package held until a fixed release ships.

Exact fixes by distribution

Debian 12 · php8.2 · NOT AFFECTED
Debian 13 · php8.4 · NOT AFFECTED
RHEL 10 · php · NOT AFFECTED
RHEL 10 · php8.4 · NOT AFFECTED
RHEL 6 · php · NOT AFFECTED
RHEL 7 · php · NOT AFFECTED
RHEL 8 · php:7.4/php · NOT AFFECTED
Verify at the official source NVD · CVE Program · Report a problem with this page
Scores and fixes here are computed automatically from those and other public sources. Confirm with the vendor advisory before changing production systems.

Quick answers

How do I fix CVE-2026-17545?

php: upgrade to 8.2.34, 8.3.35, 8.4.26, 8.5.11. Exact commands for each OS are on this page.

Is CVE-2026-17545 being exploited?

CVE-2026-17545 is not on the CISA Known Exploited Vulnerabilities list at the time of the last update. Check again, as this can change.

What does CVE-2026-17545 affect?

CVE-2026-17545 affects php. Severity is high (CVSS 7.5). On Windows, PHP's filesystem and stream APIs do not reject reserved device names such as CON, PRN, AUX, NUL, COM1 to COM9, LPT1 to LPT9, CONIN$ and CONOUT$ when they appear as a component of a path. An attacker-controlled filename therefore

How urgent is CVE-2026-17545?

Priority 42/100. High severity; Public exploit reference; Remotely exploitable, no login, no user action

Related CVEs

References

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