The recurring VPN vulnerability patterns in official advisories and vulnerability records include authentication or authorization bypass, mishandled web requests, path traversal or file access, arbitrary code execution, and denial of service. They are patterns, not a statistically complete ranking: the available evidence does not provide a consistent count across vendors and products, and the attack requirements vary from unauthenticated access to flaws that require a valid account or VPN connection.
What does “most common” mean for VPN vulnerabilities?
There is no reliable cross-vendor frequency ranking in the available official evidence. It includes agency advisories, a dated list of exploited vulnerabilities, and selected NIST National Vulnerability Database records, but not a uniform denominator that would show how often each flaw occurs across all VPN products.
It is more accurate to describe recurring vulnerability classes than to name a single “most common” flaw. A vulnerability is also different from an exposure condition: an unpatched or unsupported gateway may remain vulnerable, while weak credential protection or overly broad network access can increase the consequences of compromise without being a software vulnerability themselves.
VPN gateways matter because they are often internet-facing entry points to internal networks. In its June 2024 joint network-access guidance, CISA said it had identified more than 22 VPN-related Known Exploited Vulnerabilities associated with compromises that led to broad access to victim networks. That is the agency’s finding at publication, not a live total or a count of every VPN flaw. CISA’s 2024 network-access guidance
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Recurring VPN vulnerability patterns
| Pattern | What can happen | Example and prerequisite |
|---|---|---|
| Authentication or authorization bypass | An attacker may obtain access or reach a function that should require authorization. | NIST’s record for Palo Alto Networks PAN-OS GlobalProtect CVE-2026-0257 describes an authentication bypass that could allow an unauthorized VPN connection and notes the CVE is in CISA’s Known Exploited Vulnerabilities catalog. Cisco CVE-2025-20362 allowed access to restricted VPN URL endpoints without authentication. These are product-specific cases, not evidence that all VPNs share the flaw. NIST NVD: CVE-2026-0257; NIST NVD: CVE-2025-20362 |
| Improper input or HTTP request validation | A web-facing VPN service may mishandle crafted input, with consequences ranging from access to protected endpoints to code execution or a browser-based attack. | Cisco CVE-2025-20362 concerns improper validation of HTTP(S) input and restricted endpoint access. CVE-2025-20333 involves improper validation and authenticated code execution. CVE-2026-20069 describes invalid HTTP request handling leading to a reflected browser attack, rather than direct impact on the device. NIST NVD: CVE-2025-20362; NIST NVD: CVE-2025-20333; NIST NVD: CVE-2026-20069 |
| Path traversal and arbitrary file access | A crafted path or request may let an attacker read files outside their intended location, potentially exposing sensitive data. | A CISA/FBI 2020 advisory cited exploitation of Fortinet FortiOS SSL-VPN path traversal CVE-2018-13379. A separate 2020 exploited-vulnerability list included arbitrary file reading affecting Pulse Secure. These are historical examples; remediation depends on the current product and vendor guidance. CISA/FBI advisory on Iran-based exploitation; Joint-agency 2020 exploited-vulnerabilities list |
| Arbitrary code execution | An attacker may run code on the gateway, sometimes with high privileges; the impact and required access depend on the specific flaw. | The joint-agency 2020 list includes remote-access-related code-execution examples. Cisco CVE-2025-20333 is described by NIST as authenticated arbitrary code execution with root privileges, so it is not an unauthenticated attack. NIST NVD: CVE-2025-20333; Joint-agency 2020 exploited-vulnerabilities list |
| Denial of service | A flaw may interrupt remote access, force a device reload, or exhaust resources. | Cisco CVE-2026-20100 and CVE-2026-20105 affect Remote Access SSL VPN functionality and can cause reload or denial of service under the described conditions. Both examples require an authenticated attacker with a valid VPN connection. NIST NVD: CVE-2026-20100; NIST NVD: CVE-2026-20105 |
Can VPNs be hacked?
Yes. A vulnerability in an internet-facing gateway can provide an initial route into a network, but “VPN hacked” does not describe one universal method. A flaw may be remotely exploitable without credentials, or it may require an authenticated account, an existing VPN connection, or other conditions. For example, the cited Cisco CVE-2025-20362 and Palo Alto Networks CVE-2026-0257 records describe unauthenticated paths, while Cisco CVE-2025-20333 and the 2026 Cisco denial-of-service examples require authentication or a valid VPN connection.
VPN products also serve different purposes. These examples concern enterprise VPN gateways and remote-access services; they should not be treated as a ranking of consumer VPN privacy apps or as proof that all VPN products are equally exposed.
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Why old and unsupported VPN software remains a risk
A known flaw can remain exploitable when a gateway has not received the vendor fix or runs a release that is no longer supported. In its 2022 advisory reporting on 2021 findings, CISA and partner agencies said proof-of-concept code for most of their top exploited vulnerabilities was released within two weeks of disclosure. That is a finding about those vulnerabilities, not a guarantee that every newly disclosed flaw will have a public exploit on the same schedule. The same advisory warned that older flaws continued to be exploited:
“The exploitation of older vulnerabilities demonstrates the continued risk to organizations that fail to patch software in a timely manner or are using software that is no longer supported by a vendor.”
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CISA and partner agencies, “2021 Top Routinely Exploited Vulnerabilities” (2022)
The agencies’ 2021 report on vulnerabilities exploited in 2020 also noted that four of the top routinely exploited vulnerabilities affected remote work, VPNs, or cloud-based technologies. That is a finding about the report’s selected list, not a claim that a quarter of all vulnerabilities involve VPNs. Joint-agency 2020 exploited-vulnerabilities list
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How to reduce the risk of a vulnerable VPN gateway
- Identify the exact product and release. Keep an inventory of gateway models, software versions, exposed services, and support status so advisories can be matched to the devices actually in use.
- Follow vendor advisories and apply fixes promptly. Check whether the affected product and version match your deployment, then install the vendor’s fixed release or follow its mitigation guidance. Prioritize flaws with evidence of active exploitation, including those listed in CISA’s KEV catalog.
- Retire unsupported releases. If the vendor no longer provides security fixes, move to a supported version or replace the product; an old gateway may remain exposed even when new patches are applied elsewhere.
- Limit internet exposure. Expose only the VPN and management services needed for operation, and restrict ports and reachable interfaces where practical. CISA’s hardening guidance recommends minimizing gateway exposure and port exposure. CISA communications-infrastructure hardening guidance
- Protect accounts and review access. Use MFA and other appropriate identity controls, review accounts and access logs, and remove access that is no longer needed. These measures can reduce account-compromise risk but do not fix an unauthenticated software flaw.
- Constrain what a VPN connection can reach. Limit remote users and devices to the systems and network segments required for their work, and include remote access in broader identity, monitoring, and incident-response practices.
How to compare VPN gateway risk
A simple “secure” or “insecure” label hides important differences. When assessing two products or deployments, compare their dated vulnerability and KEV histories for the versions in use, patch speed and support lifecycle, required internet exposure, authentication and MFA options, logging visibility, and the ability to limit network access. The cited advisories and records support these as practical decision criteria, but do not provide a controlled head-to-head security comparison or establish which vendor has the highest vulnerability rate.
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