# CVE-2026-13676: fast-uri vulnerable to host confusion via failed IDN canonicalization > Attackers can bypass host-based security policies in applications using fast-uri by exploiting IDN canonicalization failures, leading to potential SSRF or access control bypasses. - **Severity:** High 7.5 (`CVSS:3.1/AV:N/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:** Over the internet - **Victim action needed:** Not needed - **Fix available:** Yes - **Published:** 29 Jun 2026 - **Updated:** 11 Sep 2026 - **Also known as:** CLEANSTART-2026-AM69167, CLEANSTART-2026-QX93902, CLSA-2026-1792402819, DEBIAN-CVE-2026-13676, ECHO-d097-f100-ef64, GHSA-4c8g-83qw-93j6, MINI-2gpr-x365-m7vg, MINI-2mp5-r3hf-9pjc, MINI-2p5w-h2f2-6vr9, MINI-46pf-hfp3-xm3h, MINI-4c69-2fxv-f88m, MINI-5c42-9mxc-g9q2, MINI-5r98-g5fg-fmmj, MINI-64mp-443p-534m, MINI-66hg-65m6-872c, MINI-6m23-mwf2-34v4, MINI-6vp2-93vg-4h6p, MINI-7fmf-jx28-38q5, MINI-7wpx-v264-m48f, MINI-89qx-xxw9-3hqr, MINI-8cjx-f3gx-v2gr, MINI-8hf2-h23x-79wv, MINI-8jcq-fq9h-qp76, MINI-9qgc-frf7-gmqm, MINI-9x69-ghrp-5jv7, MINI-chhv-3xjq-mpwh, MINI-gj47-fvfw-xg4c, MINI-h8mf-ggjv-cp7r, MINI-hhf8-45qj-7x35, MINI-j438-4xfj-c386, MINI-jhcx-7r22-5cp6, MINI-p6g7-3gph-744v, MINI-qrj2-7h8p-9j4w, MINI-r9fw-94w8-h3wc, MINI-rr6c-hwfp-pjww, MINI-v267-xhj8-6xpv, MINI-v57x-3jp9-8rj3, MINI-v7ph-7v24-3fp9, MINI-vxw7-28x9-w3vv, MINI-w62h-c4ph-x269, MINI-w82q-w649-xp8v, MINI-xr82-xcjq-x2xv, MINI-xwvx-3jxj-f7mf, ROOT-APP-NPM-CVE-2026-13676, UBUNTU-CVE-2026-13676, openSUSE-SU-2026:11160-1, openSUSE-SU-2026:21231-1 ## What is CVE-2026-13676? CVE-2026-13676 is a high-severity vulnerability in fast-uri, published on 29 Jun 2026. An attacker can exploit it over the internet without logging in, with no action from the victim. ### Official description fast-uri versions 2.3.1 through 3.1.2 and 4.0.0 fail to canonicalize Unicode (IDN) hostnames for HTTP-family URLs. The IDN conversion path calls a helper that does not exist on the global URL constructor, silently leaving the host in its original Unicode form while normalize() and equal() still return values that differ from a WHATWG-compatible URL parser. Applications that use fast-uri to enforce host-based policy (denylists, loopback filtering, redirect validation, outbound proxy routing) before passing the same URL to Node's URL or fetch can be bypassed when the two implementations resolve the same input to different hosts. Patches: upgrade to fast-uri 3.1.3 for the 3.x line or 4.0.1 for the 4.x line. Workarounds: enforce host policy using the same URL parser used for the actual request, or reject non-ASCII hosts before policy checks. Weakness: CWE-551 (Incorrect Behavior Order: Authorization Before Parsing and Canonicalization), CWE-436 (Interpretation Conflict) ## Which versions are affected by CVE-2026-13676? 6 open source packages ship an affected version, including fast-uri. It affects 1 product. | Package | Ecosystem | Affected | Fixed in | | --- | --- | --- | --- | | `fast-uri` | npm | From 2.3.1 | 2.4.2 | | `fast-uri` | npm | From 2.3.1 | 2.4.2 | | `fast-uri` | npm | From 3.0.0 | 3.1.3 | | `fast-uri` | npm | From 3.0.0 | 3.1.3 | | `fast-uri` | npm | From 4.0.0 | 4.0.1 | | `fast-uri` | npm | From 4.0.0 | 4.0.1 | | `python-pydata-sphinx-theme` | openSUSE:Leap 16.0 | All versions | 0.16.1-bp160.3.1 | | `python-pydata-sphinx-theme` | openSUSE:Tumbleweed | All versions | 0.19.0-2.1 | Products: Openjsf Fast-Uri. ## How do I fix CVE-2026-13676? Upgrade fast-uri to a fixed version for your release line: 2.4.2, 3.1.3 or 4.0.1. ## Is CVE-2026-13676 being exploited? There is no known exploitation of CVE-2026-13676 in the wild and no public exploit code. ## Other vulnerabilities in fast-uri - [CVE-2026-84292](https://insights.sbomify.com/CVE-2026-84292/): fast-uri vulnerable to authority injection via an unvalidated port in serialize (high 7.5) - [CVE-2026-84394](https://insights.sbomify.com/CVE-2026-84394/): fast-uri vulnerable to host confusion via an unclosed bracket in the URI authority (high 7.5) - [CVE-2026-75899](https://insights.sbomify.com/CVE-2026-75899/): fast-uri vulnerable to server-side request forgery via repeated hostname percent-decoding (high 7.5) - [CVE-2026-75931](https://insights.sbomify.com/CVE-2026-75931/): fast-uri vulnerable to host confusion via skipped IDN canonicalization on scheme-relative references (high 7.5) - [CVE-2026-75975](https://insights.sbomify.com/CVE-2026-75975/): fast-uri vulnerable to server-side request forgery via malformed IPv6 normalization (high 7.5) ## Fix prompt for AI coding agents ```text Check this codebase for CVE-2026-13676 and fix it if it is affected. What it is: CVE-2026-13676 is a high-severity vulnerability in fast-uri, published on 29 Jun 2026. An attacker can exploit it over the internet without logging in, with no action from the victim. Exploitation: There is no known exploitation of CVE-2026-13676 in the wild and no public exploit code. Affected packages and fixed versions: - fast-uri (npm): affected from 2.3.1; fixed in 2.4.2 - fast-uri (npm): affected from 2.3.1; fixed in 2.4.2 - fast-uri (npm): affected from 3.0.0; fixed in 3.1.3 - fast-uri (npm): affected from 3.0.0; fixed in 3.1.3 - fast-uri (npm): affected from 4.0.0; fixed in 4.0.1 - fast-uri (npm): affected from 4.0.0; fixed in 4.0.1 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-2026-13676/ (Markdown: https://insights.sbomify.com/CVE-2026-13676/index.md) ``` ## Sources - CVE record: https://www.cve.org/CVERecord?id=CVE-2026-13676 - NVD: https://nvd.nist.gov/vuln/detail/CVE-2026-13676 - OSV: https://osv.dev/vulnerability/CVE-2026-13676 --- From sbomify Insights: https://insights.sbomify.com/CVE-2026-13676/ Summaries are generated and may contain mistakes; the official description above is the record.