VulnerabilityPublished 25 Mar 2026Updated 26 Mar 2026

CVE-2026-20004: Cisco IOS XE Software · Missing Reference to Active Allocated Resource

Affects Cisco IOS XE SoftwareSource CVE Database V5

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Not known to be exploited · CVSS 7.4 High.

Data as of 30 Oct 2026, 11:52 UTC

CVSS 3.1 base score

7.4High

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

EPSS: 0.1% chance of exploitation in 30 days – higher than 8% of CVEsExploit Prediction Scoring System: the likelihood attackers will use this flaw soon.

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

Attack Vector: Adjacent
Attack Complexity: Low
Privileges Required: None
User Interaction: None
Scope: Changed
Confidentiality: None
Integrity: None
Availability: High

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

Attack Vector: Adjacent: The vulnerable component is bound to the network stack, but the attack is limited at the protocol level to a logically adjacent topology. This can mean an attack must be launched from the same shared physical (e.g., Bluetooth or IEEE 802.11) or logical (e.g., local IP subnet) network, or from within a secure or otherwise limited administrative domain (e.g., MPLS, secure VPN to an administrative network zone).
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: Changed: An exploited vulnerability can affect resources beyond the security scope managed by the security authority of the vulnerable component. In this case, the vulnerable component and the impacted component are different and managed by different security authorities.
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: High: There is total loss of availability, resulting in the attacker being able to fully deny access to resources in the impacted component; this loss is either sustained (while the attacker continues to deliver the attack) or persistent (the condition persists even after the attack has completed). Alternatively, the attacker has the ability to deny some availability, but the loss of availability presents a direct, serious consequence to the impacted component (e.g., the attacker cannot disrupt existing connections, but can prevent new connections; the attacker can repeatedly exploit a vulnerability that, in each instance of a successful attack, leaks a only small amount of memory, but after repeated exploitation causes a service to become completely unavailable).

Definitions: FIRST CVSS v3.1 specification.

Exploitation evidence

Disclosed: evidence found.
CVE published 25 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 30 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

Affected software

Product	Affected	Fixed in
CiscoCisco IOS XE Software	Affected 16.9.1 – 17.16.1a 180 affected builds	Fixed in–

AI-suggested

Organizations should immediately identify and inventory all Cisco IOS XE devices running affected versions. The primary mitigation is to apply Cisco's security patches or software updates that address this vulnerability as soon as they become available. Until patches are deployed, administrators should consider disabling local EAP authentication if it is not required, as this reduces one exploitation vector. Network segmentation should be enforced to limit adjacent network access to critical Cisco devices, restricting access to trusted management networks only. Implementing strict access control lists (ACLs) to block unauthorized TLS connection resets or suspicious repeated EAP authentication attempts can help mitigate exploitation risk. Monitoring network traffic for unusual TLS handshake patterns or repeated authentication failures can provide early detection of exploitation attempts. Additionally, enabling rate limiting on authentication requests and TLS connections may reduce the likelihood of memory exhaustion. Regularly reviewing device logs and setting up alerts for unexpected reloads or memory-related errors will aid in rapid incident response. Finally, ensure that network device configurations follow Cisco's security best practices to minimize attack surface exposure.

Description

A vulnerability in the TLS library of Cisco IOS XE Software could allow an unauthenticated, adjacent attacker to exhaust the available memory of an affected device. This vulnerability is due to improper management of memory resources during TLS connection setup. An attacker could exploit this vulnerability by repeatedly triggering the conditions that cause the memory increase. This could be done in a variety of ways, such as by repeatedly attempting Extensible Authentication Protocol (EAP) authentication when local EAP is enabled on an affected device or by using a machine-in-the-middle attack and resetting TLS connections between the affected device and other devices. A successful exploit could allow the attacker to exhaust the available memory on an affected device, resulting in an unexpected reload and a denial of service (DoS) condition.

Impact

The primary impact of CVE-2026-20004 is denial of service through memory exhaustion on Cisco IOS XE devices, which are widely deployed in enterprise and service provider networks globally. An attacker exploiting this vulnerability can cause routers and switches to reload unexpectedly, disrupting network availability and potentially causing cascading failures in dependent systems. This can affect critical network services, including VPNs, secure communications, and authentication mechanisms reliant on TLS. The disruption can lead to operational downtime, loss of productivity, and potential financial losses. Additionally, repeated device reloads may increase wear on hardware components and complicate incident response efforts. Given the vulnerability requires only adjacent network access and no authentication, attackers within the same local network or connected segments can exploit it, increasing risk in shared or multi-tenant environments. The widespread use of Cisco IOS XE in government, financial, healthcare, and telecommunications sectors means the impact could be significant across multiple critical infrastructure domains.

References

sec.cloudapps.cisco.com/security/center/content/CiscoSecurityAdvisory/cisco-sa-iosxe-tls-dos-TVgLDEZL (opens in a new tab)

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Exploitation evidence

What to do

Affected software

Description

AI analysisMachine-generated, updated 25 Mar 2026, 16:32 UTC

Technical details

References

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