How severe is CVE-2015-6421?

CVE-2015-6421 has a CVSS 3.x base score of 7.5, rated high severity. It is exploitable over network with low attack complexity, requires no privileges and no user interaction. Impact on confidentiality is none, integrity none, and availability high.

Is CVE-2015-6421 being actively exploited?

It is not currently listed in CISA's KEV catalog. Its EPSS exploit-prediction score is 2% (78th percentile), an estimate of the probability of exploitation in the next 30 days.

What products are affected by CVE-2015-6421?

CVE-2015-6421 primarily affects Cisco Wide Area Application Services. In total, 13 product configurations (CPEs) are listed as vulnerable; see the affected-products list for the exact versions.

How do I fix CVE-2015-6421?

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-2015-6421 published?

CVE-2015-6421 was published on 2016-01-27 and last updated on 2026-06-17.

CVE-2015-6421

CVE-2015-6421 is a high-severity vulnerability in Cisco Wide Area Application Services with a CVSS 3.x base score of 7.5. 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 3.x base score 7.5)
CVSS v2: 7.8
EPSS exploit prediction: 2% (78th percentile)
Actively exploited: Not listed in CISA KEV
Weakness: CWE-399
Affected product: Cisco Wide Area Application Services
Published: 2016-01-27
Last modified: 2026-06-17

Description

cifs-ao in the CIFS optimization functionality on Cisco Wide Area Application Service (WAAS) and Virtual WAAS (vWAAS) devices 5.x before 5.3.5d and 5.4 and 5.5 before 5.5.3 allows remote attackers to cause a denial of service (resource consumption and device reload) via crafted network traffic, aka Bug ID CSCus85330.

Frequently asked questions

What is CVE-2015-6421?: cifs-ao in the CIFS optimization functionality on Cisco Wide Area Application Service (WAAS) and Virtual WAAS (vWAAS) devices 5.x before 5.3.5d and 5.4 and 5.5 before 5.5.3 allows remote attackers to cause a denial of service (resource consumption and device reload) via crafted network traffic, aka Bug ID CSCus85330.
How severe is CVE-2015-6421?: CVE-2015-6421 has a CVSS 3.x base score of 7.5, rated high severity. It is exploitable over network with low attack complexity, requires no privileges and no user interaction. Impact on confidentiality is none, integrity none, and availability high.
Is CVE-2015-6421 being actively exploited?: It is not currently listed in CISA's KEV catalog. Its EPSS exploit-prediction score is 2% (78th percentile), an estimate of the probability of exploitation in the next 30 days.
What products are affected by CVE-2015-6421?: CVE-2015-6421 primarily affects Cisco Wide Area Application Services. In total, 13 product configurations (CPEs) are listed as vulnerable; see the affected-products list for the exact versions.
How do I fix CVE-2015-6421?: 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-2015-6421 published?: CVE-2015-6421 was published on 2016-01-27 and last updated on 2026-06-17.

References

Affected products (13)

cpe:2.3:a:cisco:wide_area_application_services:5.1.1:*:*:*:*:*:*:*
cpe:2.3:a:cisco:wide_area_application_services:5.1.1a:*:*:*:*:*:*:*
cpe:2.3:a:cisco:wide_area_application_services:5.1.1b:*:*:*:*:*:*:*
cpe:2.3:a:cisco:wide_area_application_services:5.1.1c:*:*:*:*:*:*:*
cpe:2.3:a:cisco:wide_area_application_services:5.1.1d:*:*:*:*:*:*:*
cpe:2.3:a:cisco:wide_area_application_services:5.2.1:*:*:*:*:*:*:*
cpe:2.3:a:cisco:wide_area_application_services:5.2_base:*:*:*:*:*:*:*
cpe:2.3:a:cisco:wide_area_application_services:5.3.1:*:*:*:*:*:*:*
cpe:2.3:a:cisco:wide_area_application_services:5.3.3:*:*:*:*:*:*:*
cpe:2.3:a:cisco:wide_area_application_services:5.3.5:*:*:*:*:*:*:*
cpe:2.3:a:cisco:wide_area_application_services:5.3.5a:*:*:*:*:*:*:*
cpe:2.3:a:cisco:wide_area_application_services:5.3.5b:*:*:*:*:*:*:*
cpe:2.3:a:cisco:wide_area_application_services:5.3.5c:*:*:*:*:*:*:*

More vulnerabilities in Cisco Wide Area Application Services

CVE-2013-3443 — Critical (CVSS 10.0): The web service framework in Cisco WAAS Software 4.x and 5.x before 5.0.3e, 5.1.x before 5.1.1c, and 5.2.x before 5.2.1…
CVE-2014-2196 — Critical (CVSS 9.3): Cisco Wide Area Application Services (WAAS) 5.1.1 before 5.1.1e, when SharePoint prefetch optimization is enabled,…
CVE-2013-3444 — Critical (CVSS 9.0): The web framework in Cisco WAAS Software before 4.x and 5.x before 5.0.3e, 5.1.x before 5.1.1c, and 5.2.x before 5.2.1;…
CVE-2007-3923 — High (CVSS 7.8): The Common Internet File System (CIFS) optimization in Cisco Wide Area Application Services (WAAS) 4.0.7 and 4.0.9, as…
CVE-2017-6628 — Medium (CVSS 6.8): A vulnerability in SMART-SSL Accelerator functionality for Cisco Wide Area Application Services (WAAS) 6.2.1, 6.2.1a,…
CVE-2018-0352 — Medium (CVSS 6.7): A vulnerability in the Disk Check Tool (disk-check.sh) for Cisco Wide Area Application Services (WAAS) Software could…

All CVEs affecting Cisco Wide Area Application Services →

Other CWE-399 (Resource Management Errors) vulnerabilities

CVE-2015-8104 — Critical (CVSS 10.0): The KVM subsystem in the Linux kernel through 4.2.6, and Xen 4.3.x through 4.6.x, allows guest OS users to cause a…
CVE-2015-0339 — Critical (CVSS 10.0): Adobe Flash Player before 13.0.0.277 and 14.x through 17.x before 17.0.0.134 on Windows and OS X and before…
CVE-2015-0335 — Critical (CVSS 10.0): Adobe Flash Player before 13.0.0.277 and 14.x through 17.x before 17.0.0.134 on Windows and OS X and before…
CVE-2015-0333 — Critical (CVSS 10.0): Adobe Flash Player before 13.0.0.277 and 14.x through 17.x before 17.0.0.134 on Windows and OS X and before…
CVE-2014-4121 — Critical (CVSS 10.0): Microsoft .NET Framework 2.0 SP2, 3.5, 3.5.1, 4, 4.5, 4.5.1, and 4.5.2 does not properly parse internationalized…
CVE-2014-0560 — Critical (CVSS 10.0): Use-after-free vulnerability in Adobe Reader and Acrobat 10.x before 10.1.12 and 11.x before 11.0.09 on Windows and OS…

Browse all CWE-399 (Resource Management Errors) vulnerabilities →