What is CVE-2026-17545?

CVE-2026-17545 is PHP on Windows: Reserved Device Names Are Not Rejected Before File/Stream I/O which can cause DoS. The supplied enrichment data classifies it as Denial of Service mapped to CWE-67 CWE-67.

Which versions are affected?

Affected product and version evidence is listed in the product table above. Current public advisories should be checked for exact version scope before patch targeting is finalized.

Is there active exploitation?

Active exploitation is not confirmed from current sources for CVE-2026-17545. If exploitation is not confirmed from current sources, teams should document that status and continue monitoring KEV, vendor, and telemetry updates.

No. CVE-2026-17545 is not listed in CISA KEV in the supplied enrichment data. KEV status should be monitored because it can change after initial disclosure or after exploitation becomes publicly confirmed.

Is there a public exploit?

4 public PoC repositories reported; 0 marked weaponized in current dataset. Public exploit or PoC availability should raise triage priority, especially for exposed or business-critical systems.

How can defenders detect it?

Start with web/proxy/WAF logs, application logs, network IDS/IPS where available. Look for vulnerability-class behavior, product errors, suspicious authentication events, exploit probes, and abnormal process activity based only on evidence that applies to the affected product.

How should teams prioritize it?

Prioritize CVE-2026-17545 using CVSS 6.9, EPSS 0%, KEV status, public PoC status, and asset exposure. Internet-facing, privileged, or business-critical deployments should be handled first.

Are workarounds available?

The supplied mitigation guidance says to apply vendor patches and restrict external exposure until fixed. Fixed-version evidence is listed in the mitigation section above.

Which threat actors are linked publicly?

No public threat actor linkage is confirmed from current sources. Do not attribute exploitation to a threat actor unless the source evidence explicitly supports that linkage.

What should be done in the next 24 hours?

Identify exposed assets running affected vendor/product/version combinations. Prioritize based on EPSS, PoC availability, and external exposure. Search available logs for exploit probes, errors, authentication anomalies, or suspicious child processes matching the vulnerability class. Open remediation tickets with affected assets, owners, evidence status, and detection coverage so decisions are traceable.

mediumDenial of Servicepublic exploit

CVE-2026-17545

CVE-2026-17545 — PHP on Windows: Reserved Device Names Are Not Rejected Before File/Stream I/O which can cause DoS

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.

Published Sep 25, 2026Updated Sep 25, 2026Sources: NVD, PHP Group (CNA), GitHub, Red Hat (VEX)

Triage

Is it exploited, how likely is exploitation, what does it touch, and how severe do the scoring sources call it.

Exploitation

Exploit code

public exploit, none observed

EPSS

Not scored

FIRST has not published a score

Affects

PHP Group

4 products listed

CVSS base

6.9

medium · 2 sources

CISA SSVC assessment

Three decision points CISA publishes for the CVEs it assesses · SSVC 2.0.3. A stakeholder decision, not a severity score.

CISA

Exploitation

PoC

none · proof-of-concept · active

Automatable

can an attacker script all four kill-chain steps

Technical impact

Partial

partial · total control of the vulnerable component

Remediation

The vendor's own words where we have them.

Upgrade PHP to a fixed release. Apply vendor patches per advisory and restrict external exposure of the affected component until patched.

Red Hat VEX · CVE-2026-17545

fixed0affected305not affected0

no_fix_planned: Out of support scope

none_available: Fix deferred

none_available: Affected

First 24 hours

Ordered from the record's own fields — exposure first, because you cannot patch what you have not found.

Identify exposed assets running affected vendor/product/version combinations.
Prioritize based on EPSS, PoC availability, and external exposure.
Search available logs for exploit probes, errors, authentication anomalies, or suspicious child processes matching the vulnerability class.

Affected scope

Vendor, product and version as the advisories word them.

Vendor	Product	Versions	Status
PHP Group	PHP	8.2.* to < 8.2.34	Vulnerable
PHP Group	PHP	8.3.* to < 8.3.35	Vulnerable
PHP Group	PHP	8.4.* to < 8.4.26	Vulnerable
PHP Group	PHP	8.5.* to < 8.5.11	Vulnerable

Attack characteristics

The CVSS vector, decoded. It describes the attack, not your exposure to it.

Attack Complexity

High

Attack Vector

Network

Privileges Req

None

User Interaction

None

Every base score collected

Sources score independently and disagree; each row says who scored it and under which version.

Score	Version	Severity	Expl.	Impact	Source
6.9	CVSS 4.0	medium	—	—	PHP Group (CNA)
5.9	CVSS 3.1	medium	—	—	Red Hat (VEX)

CVSS:4.0/AV:N/AC:H/AT:P/PR:N/UI:N/VC:N/VI:N/VA:L/SC:N/SI:N/SA:H

Weakness & attack patterns

CWE-67

Inferred from the weakness class — not observed against this CVE.

CAPEC-125 · FloodingCAPEC-130 · Excessive Allocation

Public exploit

Capability, not use: code existing is a different claim from anyone running it.

Repositories

Detection

Read off the CVSS vector and the weakness class. Starting points, not rules we have tested.

Prioritize edge telemetry for network-reachable PHP.
Monitor for scanner or exploit-pattern traffic after 4 public PoC repositories were reported.

web/proxy/WAF logsapplication logsnetwork IDS/IPS

Timeline

What happened to this CVE, newest first — with the readings a source repeats on a schedule counted underneath rather than listed.

2026
Added · CVSS 3.1 6.9 (AV:N)
Sep 25, 2026 · NVD
Initial · CVE published
Sep 25, 2026 · NVD

References

5 on the record

github.com/php/php-src/security/advisories/GHSA-9f67-6fw4-hpfp
Exploit, Third Party Advisory
access.redhat.com/security/cve/CVE-2026-17545
Vendor Advisory
bugzilla.redhat.com/show_bug.cgi?id=2541645
Vendor Advisory
www.cve.org/CVERecord?id=CVE-2026-17545
Vendor Advisory
nvd.nist.gov/vuln/detail/CVE-2026-17545
NVD

Elsewhere on this site

PHP Groupevery CVE for this vendor
Denial of Servicesame class
CWE-67other pages naming this weakness

Not in any source we poll

Listed rather than left blank: an empty field and an unmeasured one look identical on screen, and only one is a reason to look elsewhere.

No confirmed IOCs, IP addresses, domains, file hashes, or malware artifacts supplied.
No organization-specific asset inventory, compensating-control status, or patch deployment evidence supplied.
No exploit packet captures, log samples, or incident case IDs supplied.

Answered from this record1

What should defenders know first?

CVE-2026-17545 is PHP on Windows: Reserved Device Names Are Not Rejected Before File/Stream I/O which can cause DoS, a medium vulnerability affecting PHP from PHP Group. The current evidence does not list it in CISA KEV, and the exploit status is: Active exploitation is not confirmed from current sources for CVE-2026-17545. Public exploit evidence is: 4 public PoC repositories reported; 0 marked weaponized in current dataset. The affected-version evidence is listed in the key facts and affected products tables. Defenders should first verify whether exposed or business-critical assets run those versions, then apply vendor patches or mitigations, restrict reachable attack surface, and preserve logs for detection review. CVSS 6.9 describes technical severity, while EPSS 0% helps estimate near-term exploit likelihood; neither replaces asset context. Unknown fields should remain explicit in tickets, and threat actor, IOC, victimology, or payload claims should not be added unless a cited source supports them. Monitor CISA KEV, vendor advisories, NVD changes, public PoC repositories, and internal telemetry for update triggers.