How severe is CVE-2009-0635?

CVE-2009-0635 has a CVSS 2.0 base score of 7.1, rated high severity.

Is CVE-2009-0635 being actively exploited?

It is not currently listed in CISA's KEV catalog. Its EPSS exploit-prediction score is 3% (83rd percentile), an estimate of the probability of exploitation in the next 30 days.

What products are affected by CVE-2009-0635?

CVE-2009-0635 primarily affects Cisco Ios. In total, 3 product configurations (CPEs) are listed as vulnerable; see the affected-products list for the exact versions.

How do I fix CVE-2009-0635?

Review the linked vendor and NVD advisories for patched versions and mitigations, then upgrade or apply the recommended workaround. Given its high severity, prioritise patching exposed systems.

When was CVE-2009-0635 published?

CVE-2009-0635 was published on 2009-03-27 and last updated on 2026-06-16.

CVE-2009-0635

CVE-2009-0635 is a high-severity vulnerability in Cisco Ios with a CVSS 2.0 base score of 7.1. It is not currently listed as actively exploited by CISA, and its EPSS exploit-prediction score is low. The underlying weakness is classified as CWE-399.

Key facts

Severity: High (CVSS 2.0 base score 7.1)
EPSS exploit prediction: 3% (83rd percentile)
Actively exploited: Not listed in CISA KEV
Weakness: CWE-399
Affected product: Cisco Ios
Published: 2009-03-27
Last modified: 2026-06-16

Description

Memory leak in the Cisco Tunneling Control Protocol (cTCP) encapsulation feature in Cisco IOS 12.4, when an Easy VPN (aka EZVPN) server is enabled, allows remote attackers to cause a denial of service (memory consumption and device crash) via a sequence of TCP packets.

Frequently asked questions

What is CVE-2009-0635?: Memory leak in the Cisco Tunneling Control Protocol (cTCP) encapsulation feature in Cisco IOS 12.4, when an Easy VPN (aka EZVPN) server is enabled, allows remote attackers to cause a denial of service (memory consumption and device crash) via a sequence of TCP packets.
How severe is CVE-2009-0635?: CVE-2009-0635 has a CVSS 2.0 base score of 7.1, rated high severity.
Is CVE-2009-0635 being actively exploited?: It is not currently listed in CISA's KEV catalog. Its EPSS exploit-prediction score is 3% (83rd percentile), an estimate of the probability of exploitation in the next 30 days.
What products are affected by CVE-2009-0635?: CVE-2009-0635 primarily affects Cisco Ios. In total, 3 product configurations (CPEs) are listed as vulnerable; see the affected-products list for the exact versions.
How do I fix CVE-2009-0635?: Review the linked vendor and NVD advisories for patched versions and mitigations, then upgrade or apply the recommended workaround. Given its high severity, prioritise patching exposed systems.
When was CVE-2009-0635 published?: CVE-2009-0635 was published on 2009-03-27 and last updated on 2026-06-16.

References

Affected products (3)

cpe:2.3:o:cisco:ios:12.4t:*:*:*:*:*:*:*
cpe:2.3:o:cisco:ios:12.4xz:*:*:*:*:*:*:*
cpe:2.3:o:cisco:ios:12.4ya:*:*:*:*:*:*:*

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