# CVE-2021-21739: Security feature bypass in > Attackers can bypass authentication by replacing authenticated optical modules with unauthenticated ones, affecting signal transmission integrity. - **Severity:** Medium 4.6 (`CVSS:3.1/AV:P/AC:L/PR:N/UI:N/S:U/C:N/I:H/A:N`) - **Exploited in the wild:** Not known - **Login needed:** Not needed - **Attackable:** Local or same network only - **Victim action needed:** Not needed - **Fix available:** No - **Published:** 5 Aug 2021 - **Updated:** 3 Aug 2024 - **Also known as:** GHSA-2r85-x553-vqw2 ## What is CVE-2021-21739? CVE-2021-21739 is a medium-severity vulnerability in , published on 5 Aug 2021. It can only be exploited from the same machine or local network, with no action from the victim. ### Official description A ZTE's product of the transport network access layer has a security vulnerability. Because the system does not sufficiently verify the data reliability, attackers could replace an authenticated optical module on the equipment with an unauthenticated one, bypassing system authentication and detection, thus affecting signal transmission. This affects: Weakness: CWE-345 (Insufficient Verification of Data Authenticity) ## Which versions are affected by CVE-2021-21739? It affects 1 product. Products: Zte Zxctn 6120h Firmware. ## How do I fix CVE-2021-21739? No fix has been published for CVE-2021-21739 yet. Limit exposure of the affected software until one is available. ## Is CVE-2021-21739 being exploited? There is no known exploitation of CVE-2021-21739 in the wild and no public exploit code. ## Fix prompt for AI coding agents ```text Check this codebase for CVE-2021-21739 and fix it if it is affected. What it is: CVE-2021-21739 is a medium-severity vulnerability in , published on 5 Aug 2021. It can only be exploited from the same machine or local network, with no action from the victim. Exploitation: There is no known exploitation of CVE-2021-21739 in the wild and no public exploit code. Affected product: . No package-level version data is available, so check the vendor advisory linked from the reference page. Task: 1. Search the dependency manifests and lockfiles (for example package.json, package-lock.json, requirements.txt, poetry.lock, uv.lock, pom.xml, build.gradle, go.mod, Cargo.lock, Gemfile.lock) and any Dockerfiles for the affected packages, including transitive dependencies. 2. If an affected version is in use, upgrade it to the fixed version for its release line with the project's package manager, so the lockfile is regenerated. Prefer the smallest upgrade that fixes it. 3. If there is no fix, or the upgrade would break the build, do not guess: explain the risk and the safest workaround instead. 4. Run the tests and summarise what changed and why. 5. If nothing in the project is affected, say so and change nothing. Reference: https://insights.sbomify.com/CVE-2021-21739/ (Markdown: https://insights.sbomify.com/CVE-2021-21739/index.md) ``` ## Sources - CVE record: https://www.cve.org/CVERecord?id=CVE-2021-21739 - NVD: https://nvd.nist.gov/vuln/detail/CVE-2021-21739 - OSV: https://osv.dev/vulnerability/CVE-2021-21739 --- From sbomify Insights: https://insights.sbomify.com/CVE-2021-21739/ Summaries are generated and may contain mistakes; the official description above is the record.