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AsyncosOperating system · Cisco

CVE-2021-34698

HIGH · 7.5 CVSS v3.1 Published 2021-10-06
Fix available
A fix is available. Upgrade to 12.0.3-005 / 12.5.2-007 or later.
See remediation →
84/100
Remediation priority · High
Remotely reachable No privileges Zero-click

Official description Straight from the sourceThe vendor's or NVD's own wording, published unedited. Authoritative, but often terse — it says what broke, rarely what to do.

NVD · unedited
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.

Technical summary Written by usOur analysis, written from the advisory, the CVSS vector and the affected-version data. It adds context the advisory leaves out, and never invents facts that are not in the source.

dbcve analysis · high confidence

A memory exhaustion vulnerability exists in the proxy service of Cisco AsyncOS for Web Security Appliance. An unauthenticated remote attacker can exploit this by establishing a large number of HTTPS connections, causing the system to exhaust memory and stop processing new connections, resulting in denial of service.

MitigationApply the Cisco firmware patch when available; in the interim, implement connection rate limiting on the WSA proxy and consider network-level filtering to restrict abnormal connection volumes.

Verify against the referenced sources before acting — the references below are authoritative for this CVE, this summary is not.

Affected products & versions What the vendor confirmedThe version ranges the vendor confirmed as vulnerable. If your version sits inside a range here, treat yourself as exposed until you have upgraded.

NVD · CPE data
AsyncosOperating system
Affected:>= 12.0, < 12.0.3-005>= 12.5, < 12.5.2-007>= 14.0, < 14.0.1-014

CVSS breakdown How the score is builtThe industry scoring standard. It rates how the flaw is reached, what it takes to exploit, and what an attacker gains — the score is derived from those, not the other way round.

From the vector
Attack vector
Network
Complexity
Low
Privileges
None
User interaction
None
Scope
Unchanged
Confidentiality
None
Integrity
None
Availability
High

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

Am I affected? How to checkSteps we derive from the advisory and the affected-version data, so you can decide whether this CVE reaches your setup. They are a guide, not a scan — your own configuration is the authority.

dbcve checks

Work through these to decide whether this CVE applies to you.

  1. Check AsyncOS firmware version
    Access the WSA CLI and run the 'version' command, or check via the web UI under System Administration > Device Configuration
    Affected if Version falls in affected ranges: 12.0.x before 12.0.3-005, 12.5.x before 12.5.2-007, or 14.0.x before 14.0.1-014
  2. Verify proxy service is enabled
    In the WSA web UI, navigate to Security Services > Proxy Settings and confirm the proxy is enabled, or use the CLI command 'proxy status'
    Affected if Proxy service is currently enabled and running
  3. Confirm HTTPS proxy capability is active
    In the WSA web UI under Security Services > HTTPS Proxy, verify that HTTPS scanning/proxy is enabled. The vulnerability is triggered specifically through HTTPS connections
    Affected if HTTPS proxy functionality is enabled and accepting connections

A user is affected if the device runs an affected AsyncOS version listed above AND has the proxy service with HTTPS proxy capability enabled, as the attacker exploits the proxy via HTTPS connections.

Generated from the published advisory. Verify against your own configuration.

Check your environment

Paste your version and any relevant configuration and it will be compared against the affected criteria above. Do not include secrets or credentials.

AI-assisted, checked against the advisory. Informational, not a guarantee.

Remediation Closing itWhat it takes to close this. Where a vendor fix exists we point at it; where none exists we say so plainly, and can build one. Effort estimates are scoped from the advisory, not from your codebase.

dbcve · scoped
Upgrade available Upgrade to 12.0.3-005 / 12.5.2-007 / 14.0.1-014 or later
Fixed in 12.0.3-00512.5.2-00714.0.1-014
Interim mitigation

Apply the Cisco firmware patch when available; in the interim, implement connection rate limiting on the WSA proxy and consider network-level filtering to restrict abnormal connection volumes.

Recommended fix High confidence

Upgrade to AsyncOS 12.0.3-005, 12.5.2-007, 14.0.1-014 or later respective to your current branch

  1. 1. Identify the current AsyncOS version on the Cisco Web Security Appliance by running 'version' in the CLI or checking via the web UI.
  2. 2. Determine which version branch you are currently on (12.0.x, 12.5.x, or 14.0.x) to select the appropriate fixed release.
  3. 3. Back up the current device configuration using 'backup' command or the web UI before proceeding with the upgrade.
  4. 4. Download the appropriate fixed AsyncOS software version from Cisco (12.0.3-005, 12.5.2-007, or 14.0.1-014 or later) from the Cisco Software Download center.
  5. 5. Upload the new AsyncOS image to the WSA via the web UI (System Administration > Software Update) or CLI.
  6. 6. Install the upgrade and reboot the device when prompted.
  7. 7. After the device restarts, verify the new AsyncOS version is installed using 'version' command.
  8. 8. Test that the proxy service is functioning normally and monitor memory usage to confirm the memory leak is resolved.
Caveat Review Cisco release notes for your version branch for any configuration or feature changes before upgrading

Generated from the published advisory — verify against the referenced sources before acting.

Fix this in Asyncos Scoped from the published advisory
  • Consultation4.0 h
  • Implementation4.0 h
  • Testing4.0 h
  • Review / QA2.0 h
14.0 hours of engineering $2,480
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References Go to the primary sourcePrimary sources — vendor advisories, patches and trackers. Where our summary and a reference disagree, the reference wins.

Primary sources

Practitioner notes

Contributed

Peer-ranked notes from engineers who’ve handled CVE-2021-34698 in production — separate from our analysis above.

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What this is

A place for practitioners to share what actually worked: a mitigation you’ve tested, a configuration change, a version- or environment-specific caveat, or a link to a verified patch. The most useful notes rise to the top as peers upvote them, so the signal stays high.

What belongs here
  • Verified mitigations, workarounds, and config changes
  • Version or environment caveats, and links to real fixes
  • No weaponised exploit code, or anything meant to cause harm
  • No spam, self-promotion, credentials, or personal data