CISA KEV Critical Memory corruption

CVE-2026-0300 — Palo Alto Networks PAN-OS Out-of-bounds Write Vulnerability

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, 2026 · Updated Oct 15, 2026 · Sources: CISA Known Exploited Vulnerabilities, CVE Program (cve.org) e CISA ADP, NIST National Vulnerability Database, GitHub Security Advisories · CNA: palo_alto

High

Who exploits it and how urgent it is

A 0–100 score combining confirmed exploitation, ransomware and APT use, public exploits, EPSS and severity.

CISA KEV · May 6, 2026 Proofs of concept on GitHub · 10

How the score was calculated

Confirmed exploitation (CISA KEV)+35
Public exploit/PoC (github)+6
EPSS 31.7% (30-day exploitation probability)+15
Technical severity (critical)+10
Automatable exploitation (SSVC)+3

The score orders the patch queue; it does not replace your asset context (internet exposure, criticality, compensating controls).

Triage

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

Exploitation

Confirmed

CISA KEV, listed May 6, 2026

EPSS FIRST

31.73%

ahead of 98% of scored CVEs · Oct 14, 2026

Affects

Palo Alto Networks

PAN-OS and 1 more

CVSS base

9.8

Critical · 4 source(s)

CISA SSVC assessment CISA

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

Exploitation

Active

none · proof-of-concept · active

Automatable

Yes

can an attacker script the kill-chain steps

Technical impact

Total

partial · total control of the vulnerable component

Remediation

Fixes and mitigations documented by the sources — linked to the original advisory.

Documented mitigation — security.paloaltonetworks.com (NIST National Vulnerability Database)

CISA required action CISA

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.

US federal deadline: May 9, 2026 — passed 159 day(s) ago

First 24 hours

Ordered from the record’s own fields — exposure first, because you cannot patch what you have not found. A rule-generated starting point.

Identify exposed assets running the affected vendor/product/version combinations (Palo Alto Networks PAN-OS, Siemens Ruggedcom Ape1808 Firmware).
Treat as emergency remediation: the CVE is in CISA KEV (confirmed exploitation).
The attack is network-based and needs no privileges: restrict exposure (ACLs, VPN, WAF) until patched.
Apply the documented mitigations until a definitive fix is available.
EPSS ahead of 98% of scored CVEs: prioritize it in the patch queue.
Search available logs for exploit probes matching the vulnerability class (memory corruption), errors and authentication anomalies.

Affected scope

Vendor, product and versions as the sources word them.

Vendor	Product	Versions	Status	Source
Palo Alto Networks	PAN-OS	version 11.2.11version 11.2.7-h3version 11.2.7-h4version 11.2.7-h7version 11.2.7-h8version 11.2.8version 11.2.9version 11.2.10 and 154 more version 11.2.10-h1version 11.2.10-h2version 11.2.10-h3version 11.2.10-h4version 11.2.10-h5version 11.2.1version 12.1.2version 12.1.3version 12.1.4version 12.1.4-h2version 12.1.4-h3version 12.1.5version 12.1.6version 11.2.7-h12version 11.2.0version 11.2.2version 11.2.3version 11.2.4version 11.2.4-h1version 11.2.4-h10version 11.2.4-h11version 11.2.4-h12version 11.2.4-h14version 11.2.4-h15version 11.2.4-h2version 11.2.4-h4version 11.2.4-h5version 11.2.4-h6version 11.2.4-h7version 11.2.4-h8version 11.2.4-h9version 11.2.5version 11.2.6version 11.2.7version 11.2.7-h1version 11.2.7-h10version 11.2.7-h11version 11.2.7-h2version 10.2.0version 10.2.1version 10.2.2version 10.2.3version 10.2.4version 10.2.5version 10.2.6version 10.2.7version 10.2.7-h1version 10.2.7-h12version 10.2.7-h16version 10.2.7-h19version 10.2.7-h21version 10.2.7-h24version 10.2.7-h3version 10.2.7-h32version 10.2.7-h6version 10.2.7-h8version 10.2.8version 10.2.9version 10.2.10version 10.2.10-h10version 10.2.10-h12version 10.2.10-h14version 10.2.10-h17version 10.2.10-h18version 10.2.10-h2version 10.2.10-h21version 10.2.10-h27version 10.2.10-h3version 10.2.10-h30version 10.2.10-h31version 10.2.10-h4version 10.2.10-h5version 10.2.10-h7version 10.2.10-h9version 10.2.11version 10.2.12version 10.2.13version 10.2.13-h1version 10.2.13-h10version 10.2.13-h16version 10.2.13-h18version 10.2.13-h2version 10.2.13-h3version 10.2.13-h4version 10.2.13-h5version 10.2.13-h7version 10.2.14version 10.2.15version 10.2.16version 10.2.16-h1version 10.2.16-h4version 10.2.16-h6version 10.2.17version 10.2.18version 10.2.18-h1version 10.2.18-h5version 11.1.0version 11.1.1version 11.1.2version 11.1.3version 11.1.4version 11.1.4-h1version 11.1.4-h13version 11.1.4-h15version 11.1.4-h16version 11.1.4-h17version 11.1.4-h18version 11.1.4-h25version 11.1.4-h27version 11.1.4-h32version 11.1.4-h4version 11.1.4-h7version 11.1.4-h9version 11.1.5version 11.1.6version 11.1.6-h1version 11.1.6-h10version 11.1.6-h14version 11.1.6-h17version 11.1.6-h19version 11.1.6-h2version 11.1.6-h20version 11.1.6-h21version 11.1.6-h22version 11.1.6-h23version 11.1.6-h25version 11.1.6-h29version 11.1.6-h3version 11.1.6-h4version 11.1.6-h5version 11.1.6-h6version 11.1.6-h7version 11.1.7version 11.1.7-h1version 11.1.7-h2version 11.1.7-h4version 11.1.8version 11.1.9version 11.1.10version 11.1.10-h1version 11.1.10-h10version 11.1.10-h12version 11.1.10-h21version 11.1.10-h4version 11.1.10-h5version 11.1.10-h7version 11.1.10-h9version 11.1.11version 11.1.12version 11.1.13version 11.1.13-h1version 11.1.13-h2version 11.1.13-h3version 11.1.14	Vulnerable	NIST National Vulnerability Database
Palo Alto Networks	PAN-OS	≥ 12.1.0 and < 12.1.7≥ 11.2.0 and < 11.2.12≥ 11.1.0 and < 11.1.15≥ 10.2.0 and < 10.2.18-h6	Vulnerable	CVE Program (cve.org) e CISA ADP
Siemens	Ruggedcom Ape1808 Firmware	versions not specified by the source	Vulnerable	NIST National Vulnerability Database

Attack characteristics

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

Attack vector

Network

Attack complexity

Low

Privileges required

None

User interaction

None

Scope

Unchanged

Confidentiality

High

Integrity

High

Availability

High

Every base score collected

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

Score	Version	Severity	Expl.	Impact	Scored by
9.3	CVSS 4.0	Critical	—	—	psirt@paloaltonetworks.com via NIST National Vulnerability Database
9.3	CVSS 4.0	Critical	—	—	palo_alto via CVE Program (cve.org) e CISA ADP
8.7	CVSS 4.0	High	—	—	palo_alto via CVE Program (cve.org) e CISA ADP
9.8	CVSS 3.1	Critical	3.9	5.9	nvd@nist.gov via NIST National Vulnerability Database
9.8	CVSS 3.1	Critical	—	—	GitHub, Inc. via GitHub Security Advisories

CVSS:3.1/AV:N/AC:L/PR:N/UI:N/S:U/C:H/I:H/A:H (score shown at the top: nvd@nist.gov)

Weakness MITRE

Weakness class according to MITRE’s CWE catalog.

CWE-787 · Out-of-bounds Write

Other CVEs with this weakness →

CISA KEV details CISA

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

Listed

May 6, 2026

Federal deadline

May 9, 2026

passed 159 day(s) 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 reference date.

Public exploits, PoCs and detection templates

Public code that demonstrates or tests the flaw raises the odds of mass exploitation — and Nuclei templates help find vulnerable assets in your environment.

Proofs of concept on GitHub

p3Nt3st3r-sTAr/CVE-2026-0300-POC ★ 22 May 6, 2026
Security Research and Proof-of-Concept (PoC) for CVE-2026-0300 : Unauthenticated Remote Code Execution (RCE) in Palo Alto Networks PAN-OS User-ID Portal. ★ 4 May 6, 2026
A research-grade Proof-of-Concept (PoC) for CVE-2026-0300, targeting the Buffer Overflow vulnerability in Palo Alto Networks PAN-OS User-ID™ Authentication Portal (CWE-787). ★ 3 May 6, 2026
Scanner: CVE-2026-0300 PAN-OS User-ID Captive Portal Buffer Overflow RCE — Python CLI for detecting actively exploited BOF vulnerability in Palo Alto firewalls (CISA KEV 2026-05-13) ★ 2 May 22, 2026
a honeypot for CVE-2026-0300 ★ 1 May 6, 2026
CVE-2026-0300 ★ 1 May 6, 2026
PAN-OS CVE-2026-0300 Non-Destructive Exposure Survey Tool ★ 1 May 6, 2026
Read-only audit tooling for CVE-2026-0300 (PAN-OS User-ID Authentication Portal exposure) ★ 0 May 6, 2026
CVE-2026-0300 PAN-OS 12.1, 11.2, 11.1, 10.2 ★ 0 May 21, 2026
Palo Alto - CVE-2026-0300 exploit ★ 0 Aug 6, 2026

Warning: public PoCs are sometimes disguised malware. Use them only for authorized testing in an isolated environment. This portal does not host exploit code — it only points to the sources.

EPSS over time FIRST

Oct 12, 2026 → Oct 14, 2026 · 3 reading(s) · max 31.73%

Detection

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

Prioritize edge telemetry for the network-reachable component (proxy, WAF, IDS/IPS).
Correlate service crashes/restarts with inbound traffic; repeated crashes may indicate attempts.
Hunt retroactively in logs from before May 6, 2026 (KEV listing): exploitation may have started earlier.

web/proxy/WAF logsnetwork IDS/IPSendpoint telemetry (EDR)crash dumps

Timeline

What happened to this CVE, newest first.

2026
Affected products removed · 4
Oct 15, 2026 · CVE Program (cve.org) e CISA ADP
Affected products added · palo alto networks/pan-os
Oct 15, 2026 · CVE Program (cve.org) e CISA ADP
Fix documented
Oct 13, 2026 · NIST National Vulnerability Database
Affected products added · paloaltonetworks/pan-os, siemens/ruggedcom ape1808 firmware
Oct 13, 2026 · NIST National Vulnerability Database
CVSS changed · 9.3 → 9.8
Oct 13, 2026 · NIST National Vulnerability Database
Source status changed · Published → Analyzed
Oct 13, 2026 · NIST National Vulnerability Database
Record published
Oct 13, 2026
Affected products added · palo alto networks/pan-os
Oct 13, 2026 · CVE Program (cve.org) e CISA ADP
CVSS changed · 9.3
Oct 13, 2026 · CVE Program (cve.org) e CISA ADP
Source status changed · → Published
Oct 13, 2026 · CVE Program (cve.org) e CISA ADP
SSVC assessment updated
Oct 13, 2026 · CVE Program (cve.org) e CISA ADP
Added to CISA KEV (detected)
Oct 13, 2026 · CISA Known Exploited Vulnerabilities
Record created in this database
Oct 13, 2026 · CISA Known Exploited Vulnerabilities
CVE published
May 6, 2026 · palo_alto
Added to CISA KEV catalog
May 5, 2026 · CISA

Source activity

Repeated readings are counted rather than listed.

3× References added · Oct 13, 2026 – Oct 13, 2026
1× Official description updated · Oct 13, 2026 – Oct 13, 2026

References

5 on the record

security.paloaltonetworks.com/CVE-2026-0300
vendor-advisory, Mitigation, Vendor Advisory, CVE Program (cve.org) e CISA ADP
www.cisa.gov/known-exploited-vulnerabilities-catalog
US Government Resource, NIST National Vulnerability Database
cert-portal.siemens.com/productcert/html/ssa-967325.html
Third Party Advisory, NIST National Vulnerability Database
github.com/advisories/GHSA-3vfh-3cpw-2378
GitHub Security Advisories
nvd.nist.gov/vuln/detail/CVE-2026-0300
GitHub Security Advisories

Elsewhere on this site

Palo Alto Networks
every CVE for this vendor

2026-05
what else CISA listed that month

Memory corruption
same class

CWE-787
other pages naming this weakness

Related CVEs (same products)

Medium CVE-2026-0320 PAN-OS: Authenticated Admin Command Injection Vulnerability 23h
Medium CVE-2026-0318 PAN-OS: Denial of Service (DoS) on Panorama 23h
Medium CVE-2026-0319 PAN-OS: Improper Input Handling Vulnerability 23h
Low CVE-2026-0316 PAN-OS: Stored Cross-Site Scripting (XSS) Vulnerability 23h
Low CVE-2026-0317 PAN-OS: Denial of Service Vulnerability 23h
Medium CVE-2026-0321 PAN-OS: Denial of Service (DoS) Vulnerabilities in Network Services 1d

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 record

Text assembled only from the fields above — no additional claims.

What should defenders know first?

CVE-2026-0300 is "Palo Alto Networks PAN-OS Out-of-bounds Write Vulnerability", rated Critical. It affects PAN-OS (Palo Alto Networks); versions are in the scope table. It is in CISA KEV: there is evidence of real-world exploitation. CVSS 9.8 describes technical severity. EPSS 31.73% estimates the probability of exploitation in 30 days; neither replaces your asset context. First verify whether exposed or business-critical assets run the affected versions, apply vendor fixes or mitigations, and preserve logs for review.

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