VulnerabilityPublished 18 Mar 2026

CVE-2026-22321: Phoenix Contact FL SWITCH 2005 · Stack-based Buffer Overflow

Affects Phoenix Contact FL SWITCH 2005Source CVE Database V5

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Not known to be exploited · CVSS 5.3 Medium : upgrade to 3.53 when convenient.

Data as of 31 Oct 2026, 20:20 UTC

CVSS 3.1 base score

5.3Medium

How severe the flaw is on the 0–10 CVSS scale.

EPSS: 0.3% chance of exploitation in 30 days – higher than 32% of CVEsExploit Prediction Scoring System: the likelihood attackers will use this flaw soon.
Patch: Available – fixed in 3.53

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

Attack Vector: Network
Attack Complexity: Low
Privileges Required: None
User Interaction: None
Scope: Unchanged
Confidentiality: None
Integrity: None
Availability: Low

Bold values are the worst case: easiest to exploit or largest impact.

Attack Vector: Network: The vulnerable component is bound to the network stack and the set of possible attackers extends beyond the other options listed, up to and including the entire Internet. Such a vulnerability is often termed 'remotely exploitable' and can be thought of as an attack being exploitable at the protocol level one or more network hops away (e.g., across one or more routers).
Attack Complexity: Low: Specialized access conditions or extenuating circumstances do not exist. An attacker can expect repeatable success against the vulnerable component.
Privileges Required: None: The attacker is unauthorized prior to attack, and therefore does not require any access to settings or files to carry out an attack.
User Interaction: None: The vulnerable system can be exploited without any interaction from any user.
Scope: Unchanged: An exploited vulnerability can only affect resources managed by the same security authority. In this case, the vulnerable component and the impacted component are either the same, or both are managed by the same security authority.
Confidentiality: None: There is no loss of confidentiality within the impacted component.
Integrity: None: There is no loss of integrity within the impacted component.
Availability: Low: Performance is reduced or there are interruptions in resource availability. Even if repeated exploitation of the vulnerability is possible, the attacker does not have the ability to completely deny service to legitimate users. The resources in the impacted component are either partially available all of the time, or fully available only some of the time, but overall there is no direct, serious consequence to the impacted component.

Definitions: FIRST CVSS v3.1 specification.

Exploitation evidence

Disclosed: evidence found.
CVE published 18 Mar 2026
Detectable: no evidence on record.
No public nuclei template indexed
Weaponized: no evidence on record.
No public exploit code indexed in Metasploit or Exploit-DB
Exploited in the wildExploited: no evidence on record.
Not in CISA KEV and no source reports exploitation
Observed by OffSeq MirageSeen by Mirage: no evidence on record.
No attack traffic recorded by OffSeq Mirage sensors

A missing step is not evidence of safety. Sources: cve.org (opens in a new tab), the Metasploit, Exploit-DB and nuclei-templates index as of 31 Oct 2026.

Disclosed: The CVE record is public on cve.org. Its publication is t = 0.
Detectable: A public nuclei template can find exposed instances, for defenders and attackers alike.
Weaponized: A Metasploit exploit module or Exploit-DB entry exists (Metasploit scanner modules do not count), or CISA SSVC or the CVSS exploit maturity reports a public proof of concept.
Exploited in the wild: CISA KEV lists it, CISA SSVC rates exploitation active, or a source reports attacks.
Observed by OffSeq Mirage: OffSeq Mirage honeypot sensors recorded attack traffic for this CVE, or found exposed hosts without attack traffic.

Moments are spaced evenly, not to scale; a dashed line marks a gap of six months or more. Deltas count from t = 0. Sources that give only a date (CISA KEV, Exploit-DB, or a time of exactly 00:00Z) read “same day” rather than hours. Metasploit modules carry the flaw’s disclosure date, not their release date, and nuclei templates carry no date, so both appear above but not on the timeline.

What to do

Upgrade FL to 3.53.

Affected software

Product	Affected	Fixed in
Phoenix ContactFL SWITCH 2005	Affected <3.53	Fixed in 3.53
Phoenix ContactFL SWITCH 2008	Affected <3.53	Fixed in 3.53
Phoenix ContactFL SWITCH 2016	Affected <3.53	Fixed in 3.53
Phoenix ContactFL SWITCH 2105	Affected <3.53	Fixed in 3.53
Phoenix ContactFL SWITCH 2108	Affected <3.53	Fixed in 3.53
Phoenix ContactFL SWITCH 2116	Affected <3.53	Fixed in 3.53

AI-suggested

To mitigate CVE-2026-22321, organizations should first monitor Phoenix Contact’s advisories for official patches or firmware updates addressing this vulnerability and apply them promptly once available. In the absence of patches, network segmentation and access control lists (ACLs) should be implemented to restrict Telnet and SSH access to trusted management networks or specific IP addresses, minimizing exposure to unauthenticated attackers. Disabling Telnet in favor of more secure management protocols, if feasible, can reduce attack surface. Employing network intrusion detection systems (NIDS) to monitor for anomalous oversized username inputs or repeated login failures may help detect exploitation attempts. Additionally, administrators should consider implementing rate limiting on login attempts to reduce the risk of repeated DoS triggers. Regularly auditing and hardening device configurations, including disabling unused services and enforcing strong authentication policies, will further reduce risk. Finally, maintaining an incident response plan that includes procedures for managing temporary loss of remote access is advisable.

Description

A stack-based buffer overflow in the device's Telnet/SSH CLI login routine occurs when a unauthenticated attacker send an oversized or unexpected username input. An overflow condition crashes the thread handling the login attempt, forcing the session to close. Because other CLI sessions remain unaffected, the impact is limited to a low‑severity availability disruption.

Impact

The primary impact of CVE-2026-22321 is a limited denial of service (DoS) affecting the availability of individual Telnet/SSH login sessions on Phoenix Contact FL SWITCH 2005 devices. This could disrupt remote management access temporarily, potentially delaying administrative tasks or incident response actions. Since other CLI sessions and device functions remain unaffected, the overall operational impact is low. However, in environments where continuous remote management access is critical—such as industrial control systems, manufacturing plants, or critical infrastructure—this disruption could increase operational risk or complicate troubleshooting. The vulnerability does not compromise confidentiality or integrity, so data theft or manipulation is not a concern. The ease of exploitation (no authentication or user interaction required) means attackers with network access to the management interface could trigger the condition at will. While no exploits are known in the wild, the vulnerability could be used as part of a broader attack strategy to degrade network device availability or as a distraction during more severe attacks.

CWE-121Stack-based Buffer Overflow (opens in a new tab)
Variant weaknessLikelihood of exploit: HighCWE Top 25 (2025): #14
The product writes past the end of a buffer that was allocated on the stack.
Operation · Build and Compilation · Environment Hardening
Use automatic buffer overflow detection mechanisms that are offered by certain compilers or compiler extensions. Examples include: the Microsoft Visual Studio /GS flag, Fedora/Red Hat FORTIFY_SOURCE GCC flag, StackGuard, and ProPolice, which provide various mechanisms including canary-based detection and range/index…
Architecture and Design
Use an abstraction library to abstract away risky APIs. Not a complete solution.
Implementation
Implement and perform bounds checking on input.
OWASP Cheat Sheets
XML Security (opens in a new tab)
Mass Assignment (opens in a new tab)
OWASP ASVS 4.0.3
V13.3.1 (opens in a new tab)
V5.1.4 (opens in a new tab)
V5.1.3 (opens in a new tab)
From MITRE CWE, MITRE CAPEC and OWASP (Top 10, OpenCRE).

References

certvde.com/de/advisories/VDE-2025-104 (opens in a new tab)

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Exploitation evidence

What to do

Affected software

Description

AI analysisMachine-generated, updated 18 Mar 2026, 07:58 UTC

WeaknessesCWE-121

Technical details

References

Community reviews

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