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Stack-based Buffer OverflowWeakness · CWE-121

CVE-2026-51603

HIGH · 7.5 CVSS v3.1 Published 2026-07-09
Mitigation only
No fix yet — a mitigation exists. There is no fixed release. A documented workaround reduces exposure in the meantime.
See remediation →
84/100
Remediation priority · High
Remotely reachable No privileges Zero-click 6 weeks old

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 stack-based buffer overflow vulnerability in the RTSP service of Tenda CP3 V3.0 (firmware V31.1.9.91) allows an unauthenticated remote attacker to cause a denial of service via a crafted second SETUP request. After completing the OPTIONS, DESCRIBE, and a legitimate first SETUP request to obtain a valid session ID, the RTSP service's second-stage URL routing parser fails to validate the length of the URL field in the subsequent SETUP request. By supplying a URL consisting of exactly four consecutive repetitions of a valid RTSP URL, an attacker can bypass first-stage format validation and trigger a stack buffer overflow, causing an immediate crash of the RTSP service process and rendering the device inaccessible to all clients on the local network.

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

Stack-based buffer overflow in Tenda CP3 V3.0 RTSP service's second-stage URL routing parser. After completing valid RTSP handshake (OPTIONS, DESCRIBE, first SETUP) to obtain a session ID, sending a second SETUP request with a URL containing exactly four consecutive repetitions of a valid RTSP URL bypasses first-stage validation and overflows a stack buffer, causing immediate service crash.

MitigationApply network segmentation to isolate affected device; disable RTSP service if unnecessary; contact Tenda for firmware update; implement IDS/IPS rules to detect RTSP anomaly patterns.

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

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. Identify Tenda CP3 firmware version
    Log into the device web UI and look under 'Device Info' for the firmware version, or run 'cat /proc/version' via telnet/SSH if you have console access.
    Affected if The firmware version is 3.0 (the version listed as affected).
  2. Verify RTSP service is enabled and listening
    Run 'netstat -tlnp | grep 554' or use nmap to scan port 554 on the device IP.
    Affected if RTSP service is listening on port 554 (or the default RTSP port).
  3. Confirm RTSP handshake completes and yields a session ID
    Send an RTSP OPTIONS request, followed by DESCRIBE and a first SETUP using a standard RTSP client (e.g., VLC or a script). Verify a session ID is returned.
    Affected if The device returns a valid RTSP session ID after the initial handshake, indicating the RTSP service is active.
  4. Inspect RTSP traffic for the malicious second SETUP pattern
    Capture network traffic on the device or at the switch using tcpdump or Wireshark. Look for a second SETUP request that contains a URL with exactly four consecutive repetitions of a valid RTSP URL (e.g., 'rtsp://example.com/').
    Affected if Such a packet is observed in the capture.
  5. Check for RTSP service crash logs
    Review the device's system logs (e.g., /var/log/messages, syslog, or the web UI's 'Log' page) for entries indicating the RTSP process has crashed or restarted after the above packet was sent.
    Affected if The logs show a crash or unexpected restart of the RTSP service correlated with the pattern.

If the device runs Tenda CP3 firmware V3.0, has RTSP listening on port 554, and the service crashes after receiving a second SETUP request with a URL containing exactly four consecutive repetitions, the environment is affected by CVE-2026-51603.

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

Apply network segmentation to isolate affected device; disable RTSP service if unnecessary; contact Tenda for firmware update; implement IDS/IPS rules to detect RTSP anomaly patterns.

Have this fixed Scoped from the published advisory
  • Consultation4.0 h
  • Implementation16.0 h
  • Testing8.0 h
  • Review / QA4.0 h
32.0 hours of engineering $5,600
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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-2026-51603 in production — separate from our analysis above.

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