What is CVE-2026-0300?

CVE-2026-0300 is PAN-OS: Unauthenticated user initiated Buffer Overflow Vulnerability in User-ID™ Authentication Portal. The supplied enrichment data classifies it as Remote Code Exec mapped to CWE-787 CWE-787.

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?

Yes: CISA KEV signal present. If exploitation is not confirmed from current sources, teams should document that status and continue monitoring KEV, vendor, and telemetry updates.

Is there a public exploit?

74 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, EDR process telemetry, host service logs 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-2026-0300 using CVSS 9.8, EPSS 32%, KEV status, public PoC status, and asset exposure. Internet-facing, privileged, or business-critical deployments should be handled first.

Are workarounds available?

Workarounds are not confirmed from current sources. 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. Treat as emergency remediation because CISA KEV status is present. 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.

CISA KEVcriticalRemote Code Execpublic exploit

CVE-2026-0300

PAN-OS: Unauthenticated user initiated Buffer Overflow Vulnerability in User-ID™ Authentication Portal

Q: Is it in CISA KEV?

Yes. The supplied enrichment data lists CVE-2026-0300 in CISA KEV with required action: Apply mitigations per vendor instructions, follow applicable BOD 22-01 guidance for cloud services, or discontinue use of the product if mitigations are unavailable. Until the vendor releases an official fix, the following workaround should be implemented: - Restrict User-ID Authentication Portal access to only trusted zones. - Disable User-ID Authentication Portal if not required. 5/13/2026: Palo Alto has released a variety of patches. If these are relevant to your environment, please apply the designated patch.. KEV status should be monitored because it can change after initial disclosure or after exploitation becomes publicly confirmed.

A buffer overflow vulnerability in the User-ID™ Authentication Portal (aka Captive Portal) service of Palo Alto Networks PAN-OS software allows an unauthenticated attacker to execute arbitrary code with root privileges on the PA-Series and VM-Series firewalls by sending specially crafted packets. The risk of this issue is greatly reduced if you secure access to the User-ID™ Authentication Portal per the best practice guidelines https://knowledgebase.paloaltonetworks.com/KCSArticleDetail by restricting access to only trusted internal IP addresses. Prisma Access, Cloud NGFW and Panorama appliances are not impacted by this vulnerability.

Published May 6, 2026Updated Jun 17, 2026Sources: NVD, Palo Alto Networks (CNA), CISA, FIRST EPSS, GitHub, GitHub Security Advisory

Triage

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

Exploitation

Confirmed

CISA KEV, listed May 6, 2026

EPSS

32%

ahead of 98% of scored CVEs

Affects

Palo Alto

6 products listed

CVSS base

9.8

critical · 3 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

Active

none · proof-of-concept · active

Automatable

Yes

can an attacker script all four kill-chain steps

Technical impact

Total

partial · total control of the vulnerable component

Remediation

The vendor's own words where we have them.

This issue will be fixed in upcoming releases of PAN-OS as captured in the table above. We strongly recommend that you secure access to your User-ID™ Authentication Portal following the instructions in the workarounds section below.

CISA required action

Apply mitigations per vendor instructions, follow applicable BOD 22-01 guidance for cloud services, or discontinue use of the product if mitigations are unavailable. Until the vendor releases an official fix, the following workaround should be implemented: - Restrict User-ID Authentication Portal access to only trusted zones. - Disable User-ID Authentication Portal if not required. 5/13/2026: Palo Alto has released a variety of patches. If these are relevant to your environment, please apply the designated patch.

Federal deadline May 9, 2026 — passed 106 days ago

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.
Treat as emergency remediation because CISA KEV status is present.
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
Palo Alto	Cloud NGFW	All	Patched
Palo Alto	PAN-OS	12.1.0 to < 12.1.7	Vulnerable
Palo Alto	PAN-OS	11.2.0 to < 11.2.12	Vulnerable
Palo Alto	PAN-OS	11.1.0 to < 11.1.15	Vulnerable
Palo Alto	PAN-OS	10.2.0 to < 10.2.18-h6	Vulnerable
Palo Alto	Prisma Access	All	Patched

Attack characteristics

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

Availability

High

Confidentiality

High

Integrity

High

Scope

Unchanged

Attack Complexity

Low

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
9.8	CVSS 3.1	critical	3.9	5.9	NVD, GHSA
9.3	CVSS 4.0	critical	—	—	Palo Alto Networks (CNA)
8.7	CVSS 4.0	high	—	—	Palo Alto Networks (CNA)

CVSS:3.1/AV:N/AC:L/PR:N/UI:N/S:U/C:H/I:H/A:H

Weakness & attack patterns

CWE-787

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

CAPEC-242 · Code InjectionCAPEC-35 · Leverage Executable Code in Non-Executable Files

CISA KEV details

CISA lists a CVE here once it has evidence of exploitation against real targets.

CISAThat month →

Listed

May 6, 2026

Federal deadline

May 9, 2026

passed 106 days ago

Ransomware use

Unknown

CISA records ransomware use only for campaigns it has confirmed, so “Unknown” means unrecorded, not ruled out. The deadline binds US federal agencies; for everyone else it is a date to argue against.

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.

Search application, proxy, and WAF logs for requests touching //knowledgebase.paloaltonetworks.com/KCSArticleDetail.
Prioritize edge telemetry for network-reachable Cloud NGFW, PAN-OS, Prisma Access.
Monitor for scanner or exploit-pattern traffic after 74 public PoC repositories were reported.

web/proxy/WAF logsapplication logsnetwork IDS/IPSEDR process telemetryhost service logs

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 9.8 (AV:N)
Jun 17, 2026 · NVD
Added to CISA KEV catalog
May 6, 2026 · CISA
Initial · CVE published
May 6, 2026 · NVD
Reported · Updated with Threat Prevention ID and clarified the Required Configuration section.
May 6, 2026 · Palo Alto Networks
Added · GHSA-3vfh-3cpw-2378 published (critical)
May 6, 2026 · GitHub Security Advisory
Reported · Initial publication.
May 5, 2026 · Palo Alto Networks

References

5 on the record

security.paloaltonetworks.com/CVE-2026-0300
Mitigation, Vendor Advisory
cert-portal.siemens.com/productcert/html/ssa-967325.html
Third Party Advisory
www.cisa.gov/known-exploited-vulnerabilities-catalog?field_cve=CVE-2026-0300
US Government Resource
nvd.nist.gov/vuln/detail/CVE-2026-0300
NVD, Vendor Advisory
github.com/advisories/GHSA-3vfh-3cpw-2378
Exploit, Third Party Advisory

Coverage

1 story from the feeds we poll

The Agentic AI threat cluster: Seven incidents, three actors, and what they mean for your exposure
Tenable Blog · Aug 15, 2026

Elsewhere on this site

Palo Altoevery CVE for this vendor
May 2026what else CISA listed
Remote Code Execsame class
CWE-787other 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-2026-0300 is PAN-OS: Unauthenticated user initiated Buffer Overflow Vulnerability in User-ID™ Authentication Portal, a critical vulnerability affecting Cloud NGFW, PAN-OS, Prisma Access from Palo Alto Networks. The current evidence lists it in CISA KEV, and the exploit status is: Yes: CISA KEV signal present. Public exploit evidence is: 74 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 9.8 describes technical severity, while EPSS 32% 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.