Cisco Web Security Appliance Proxy Service Denial of Service Vulnerability
Noroxi assessment
Priority: Monitor (action score 30/100)
- The sources we track (CISA KEV, Exploit-DB, Metasploit, Nuclei, GitHub) show no public exploit code or exploitation in the wild.
- Probability of exploitation in the next 30 days: 1.4% (FIRST EPSS); higher than 72.6% of all records.
- Anyone who can reach it over the internet can trigger it. No account or password is required. No user action is required. No special conditions are required; it is repeatable.
- According to CISA the attack is automatable: targets can be found by mass scanning.
- According to the record, no fixed version is available yet.
- Mentioned 1 time in Turkish national cyber security advisories (siberguvenlik.gov.tr).
Low priority for now. Update when a fix is released; follow the vendor's advisory.
Generated automatically from the record's data: CVSS (NVD and CNA), CISA KEV and SSVC, FIRST EPSS, exploit sources, fixed versions. How we calculate it
Primary sources: NVD · CVE.org · FIRST EPSS
A vulnerability in the proxy service of Cisco AsyncOS for Cisco Web Security Appliance (WSA) could allow an unauthenticated, remote attacker to exhaust system memory and cause a denial of service (DoS) condition on an affected device. This vulnerability is due to improper memory management in the proxy service of an affected device. An attacker could exploit this vulnerability by establishing a large number of HTTPS connections to the affected device. A successful exploit could allow the attacker to cause the system to stop processing new connections, which could result in a DoS condition. Note: Manual intervention may be required to recover from this situation.
- Published
- Oct 6, 2021
- Updated
- Jun 16, 2026
- EPSS
- 1.4% · 72th percentile
- CWE
- CWE-401
Report tools
Action score
30
Monitor
Low priority for now.
- CVSS
- 30 / 40 · 7.5 / 10
- CISA KEV
- 0 / 30 · Not listed
- EPSS
- 0 / 30 · 1.4%
CISA SSVC decision
- Exploitation
- none
- Automatable
- yes
- Technical impact
- total
Vulnrichment: CISA's decision-tree inputs.
CNA vs NVD score
- NVD
- 7.5
- CNA · cisco
- 8.6
- 1.1 point gap
CVSS:3.1/AV:N/AC:L/PR:N/UI:N/S:C/C:N/I:N/A:H
The score given by the assigning authority versus NVD’s independent score. A gap means the severity is contested.
Get told when this record changes
- Not in KEV: no record of exploitation in the wild
- No public exploit code on record
- No fixed version yet
If any of these changes, we'll tell you in the daily email digest.
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Noroxi analysis
What does it mean in your environment?
The assessment above is generated automatically from the record's data; it doesn't know your environment. Our team verifies on your systems whether this vulnerability is actually exploitable and which mitigation is enough.
We use this product, ask for helpAffected systems
Is your version affected?
Pick the product and type the version you run. It's compared with this record's version ranges in your browser; the version isn't sent anywhere.
| Vendor | Product | CPE |
|---|---|---|
| cisco | asyncos | cpe:2.3:o:cisco:asyncos |
| cisco | web security appliance s170 | cpe:2.3:h:cisco:web_security_appliance_s170 |
| cisco | web security appliance s190 | cpe:2.3:h:cisco:web_security_appliance_s190 |
| cisco | web security appliance s380 | cpe:2.3:h:cisco:web_security_appliance_s380 |
| cisco | web security appliance s390 | cpe:2.3:h:cisco:web_security_appliance_s390 |
| cisco | web security appliance s680 | cpe:2.3:h:cisco:web_security_appliance_s680 |
| cisco | web security appliance s690 | cpe:2.3:h:cisco:web_security_appliance_s690 |
| cisco | web security appliance s690x | cpe:2.3:h:cisco:web_security_appliance_s690x |
Affected versions
NVD version ranges (for catalog products). Add the product to your stack with a version and matching uses these.
- cisco asyncos12.0 and later · before 12.0.3-005
- cisco asyncos12.5 and later · before 12.5.2-007
- cisco asyncos14.0 and later · before 14.0.1-014
Versions reported by the vendor
Affected version ranges reported by the assigning authority (cisco). Independent of NVD's CPE analysis and usually ahead of it.
Cisco Cisco Web Security Appliance (WSA)
- n/aaffected
Same product
cisco: all recordsOther highest-scoring records for the same primary product.
- CVE-2025-20393Cisco Secure Email Gateway and Cisco Secure Email and Web Manager Remote Command Execution VulnerabilityKEV80Now
- CVE-2026-76461Cisco Secure Email Gateway SQL Injection VulnerabilityKEV78This week
- CVE-2026-76519Cisco Secure Email Gateway Arbitrary File Write VulnerabilityKEV69This week
Published before and after this one in the same product
- ← EarlierCVE-2020-3367Nov 18, 2020 · Cisco Secure Web Appliance Privilege Escalation Vulnerability31Monitor
- ← EarlierCVE-2021-1534Oct 6, 2021 · Cisco Email Security Appliance URL Filtering Bypass Vulnerability21Monitor
- Later →CVE-2021-34741Nov 4, 2021 · Cisco Email Security Appliance Denial of Service Vulnerability30Monitor
Remediation
Which version to upgrade to
Fix versions compiled from the vendor, package registries and Microsoft. Verify the vendor's note before upgrading.
No fix version is recorded for this entry. Check the references for vendor advisories.
Exploit status
No known public exploit
No public exploit has been observed yet. That doesn't mean you're safe, only that the bar is a little higher.
Research context
For pentesters and researchers: attack profile, score disagreement, timeline, patch commits, credits, variant and chain candidates, bug bounty scope. All derived from existing data; no exploit code.
Timeline
From publication to today: proof of concept, Metasploit module, CISA KEV and fix record. Dates are as reported by the sources.
No dated events beyond publication.
FIRST EPSS daily score; only changes of 0.01 or more are recorded (step chart).
Patch and commit links
Commit, PR and diff links among the references. A starting point for patch-diffing and variant hunting; fixes, not exploits.
No commit or PR link among the references.
Credits
All researchersFinders, reporters and analysts named in the CNA record. Click a name for that researcher’s other records.
No credits in the CNA record.
Variant candidates
Same product, same weakness class, within 18 months. If the patch missed the root cause, the sibling bug is here.
No nightly-computed relations.
Chain candidates
An authentication bypass and a privilege-requiring bug in the same product, published close together: combined they may become an unauthenticated path.
—
Bug bounty scope
No known public program.
Source: bounty-targets-data (public HackerOne, Bugcrowd, Intigriti, YesWeHack listings).
National notice (Türkiye Cybersecurity Directorate / USOM)
Official security notices citing this record; remediation advice is on the agency's page.
- TR-21-0814 · Oct 7, 2021(Cisco Güvenlik Zafiyeti)
Technical details
Attack conditions
- Anyone who can reach it over the internet can trigger it.
- No account or password is required.
- No user action is required.
- No special conditions are required; it is repeatable.
If successful
- Confidentiality
- none
- Integrity
- none
- Availability
- high · the service can be disrupted
- Attack vector
- Network
- Attack complexity
- Low
- Privileges required
- None
- User interaction
- None
- Scope
- Unchanged
- Confidentiality impact
- None
- Integrity impact
- None
- Availability impact
- High
Weakness class (CWE)
CWE-401 · Missing Release of Memory after Effective LifetimeCVSS vector
CVSS:3.1/AV:N/AC:L/PR:N/UI:N/S:U/C:N/I:N/A:H
nvd-primary
Attack context
MITRE CAPEC attack patterns and ATT&CK techniques for this weakness class (CWE). A starting point for detection rules and threat hunting.
MITRE has no CAPEC/ATT&CK mapping for this CWE.
Change log
No changes recorded on tracked fields yet. Score, KEV, exploit maturity and fix status changes appear here.
References
Vendor advisories and official records. Exploit/PoC links are deliberately left out.