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Adaptive Security Appliance 5505 FirmwareOperating system · Cisco

CVE-2017-12373

MEDIUM · 5.9 CVSS v3.0 Published 2017-12-15
Mitigation only
No fix yet — a mitigation exists. There is no fixed release. A documented workaround reduces exposure in the meantime.
See remediation →
68/100
Remediation priority · Elevated
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 TLS protocol implementation of legacy Cisco ASA 5500 Series (ASA 5505, 5510, 5520, 5540, and 5550) devices could allow an unauthenticated, remote attacker to access sensitive information, aka a Return of Bleichenbacher's Oracle Threat (ROBOT) attack. An attacker could iteratively query a server running a vulnerable TLS stack implementation to perform cryptanalytic operations that may allow decryption of previously captured TLS sessions. Cisco Bug IDs: CSCvg97652.

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

This is a ROCE vulnerability in the TLS implementation of legacy Cisco ASA 5500 Series devices. The vulnerability allows an unauthenticated remote attacker to perform cryptanalytic operations similar to the original Bleichenbacher attack by iteratively querying the server and observing TLS error responses, ultimately enabling decryption of previously captured TLS sessions using RSA key exchange.

MitigationUpgrade affected Cisco ASA devices to a patched software version, or if devices are end-of-life, replace them with current hardware. Alternatively, disable RSA key exchange ciphers and enforce forward-secret cipher suites like ECDHE.

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
Adaptive Security Appliance 5505 FirmwareOperating system
Affected:all versions
Adaptive Security Appliance 5510 FirmwareOperating system
Affected:all versions
Adaptive Security Appliance 5520 FirmwareOperating system
Affected:all versions
Adaptive Security Appliance 5540 FirmwareOperating system
Affected:all versions
Adaptive Security Appliance 5550 FirmwareOperating system
Affected:all versions

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
High
Privileges
None
User interaction
None
Scope
Unchanged
Confidentiality
High
Integrity
None
Availability
None

CVSS:3.0/AV:N/AC:H/PR:N/UI:N/S:U/C:H/I:N/A:N

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. Identify the ASA device model
    Run 'show version' on the device CLI and look for the hardware model string in the output
    Affected if The model is Cisco ASA 5505, 5510, 5520, 5540, or 5550
  2. Confirm firmware version
    Run 'show version' and locate the firmware version line
    Affected if The device is one of the affected models AND is running any firmware version (all versions are affected)
  3. Verify RSA key exchange is enabled
    Check the TLS cipher configuration with 'show run all ssl' or examine the crypto ipsec ikev1/ipsec commands for RSA-based key exchange methods
    Affected if RSA key exchange ciphers (such as RSA-RC4-MD5, RSA-3DES-SHA, etc.) are configured and enabled in the TLS/SSL settings
  4. Check for TLS error response differences
    Send test TLS ClientHello messages with invalid RSA-encrypted premaster secrets and observe whether the device returns distinguishable error messages (e.g., different alerts for decryption failure vs. format errors)
    Affected if The device returns varying TLS alert messages that could serve as a Bleichenbacher oracle, allowing iterative cryptanalytic queries

You are affected if you have a Cisco ASA 5505, 5510, 5520, 5540, or 5550 in production with RSA key exchange enabled and the device reveals distinguishable TLS error responses.

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.

From vendor data
Mitigation available No clean upgrade yet — mitigate in the meantime
Mitigation

Upgrade affected Cisco ASA devices to a patched software version, or if devices are end-of-life, replace them with current hardware. Alternatively, disable RSA key exchange ciphers and enforce forward-secret cipher suites like ECDHE.

Fix this in Adaptive Security Appliance 5505 Firmware Scoped from the published advisory
  • Consultation4.0 h
  • Implementation8.0 h
  • Testing3.0 h
  • Review / QA2.0 h
17.0 hours of engineering $3,050
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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-2017-12373 in production — separate from our analysis above.

No notes yet

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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
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  • No spam, self-promotion, credentials, or personal data