# CVE-2026-75899: fast-uri vulnerable to server-side request forgery via repeated hostname percent-decoding > An attacker can bypass host-policy checks and trigger server-side request forgery by exploiting double percent-decoding in the fast-uri library. - **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:** 24 Aug 2026 - **Updated:** 24 Aug 2026 - **Also known as:** CLEANSTART-2026-GK02721, CLEANSTART-2026-NC17726, CLEANSTART-2026-PV08936, CLEANSTART-2026-SR09955, CLSA-2026-1792762888, DEBIAN-CVE-2026-75899, ECHO-056e-32dc-52a2, GHSA-fph4-wmhf-6fwf, MINI-2q85-qgq3-5x9v, MINI-362p-gg77-529q, MINI-5633-rvv2-9mv5, MINI-6fhx-pvmm-gwfj, MINI-6j9w-p2wr-mv8h, MINI-7656-25mj-r42c, MINI-7f82-2cfq-gfp2, MINI-7r63-pj3q-228f, MINI-7w9w-x3x6-q5gc, MINI-8w5r-74pp-v5fh, MINI-9f7h-vv92-92r3, MINI-9qg4-f2wj-rfch, MINI-c9fj-q3gr-2mgq, MINI-cgvq-v9hj-8wm6, MINI-h392-9m6w-77q8, MINI-h5qp-h42c-3975, MINI-h5xj-c26v-m6x8, MINI-hggr-vmp4-5fx9, MINI-j7xh-539m-q6hx, MINI-jcj7-gqf7-xm4q, MINI-jf46-7whm-gg42, MINI-m2w6-6938-hxm2, MINI-mqm9-8w68-vfhq, MINI-p3m6-c6f8-p462, MINI-qchj-8927-xpw8, MINI-qg9v-47h7-fj23, MINI-rxm6-p88g-vgv2, MINI-vf59-p8wx-88wq, MINI-vvrx-hpfv-xv9j, MINI-xp6j-4jpv-vm3j, ROOT-APP-NPM-CVE-2026-75899, UBUNTU-CVE-2026-75899 ## What is CVE-2026-75899? CVE-2026-75899 is a high-severity server-side request forgery vulnerability in fast-uri, published on 24 Aug 2026. An attacker can exploit it over the internet without logging in, with no action from the victim. ### Official description fast-uri is a URI parser for Node.js. It decodes percent escapes in a hostname during parsing and then decodes the parsed hostname a second time during authority recomposition, so a single call to normalize or resolve can turn nested percent-encoded input into a different network destination such as a loopback hostname or address. For example, a doubly encoded host that spells out a loopback name decodes to that live host in one operation, which contradicts RFC 3986 section 2.4 that an implementation must not decode the same string more than once. An application that normalizes or resolves an untrusted HTTP-family URI before outbound routing, redirect validation, or a host-policy check can receive a destination different from the one the original encoded host represented, giving a server-side request forgery and host-policy bypass primitive. This is an incomplete-fix variant of CVE-2026-6322. The affected versions are 2.4.1 up to but not including 2.4.5, 3.1.2 up to but not including 3.1.6, and 4.0.0 up to but not including 4.1.3. The issue is fixed in 2.4.5, 3.1.6, and 4.1.3, which normalize percent escapes once and preserve encoded percent signs. Users should upgrade to a patched version. Weakness: CWE-918 (Server-Side Request Forgery), CWE-174 (Double Decoding of the Same Data) ## Which versions are affected by CVE-2026-75899? 6 open source packages ship an affected version, including fast-uri. It affects 1 product. | Package | Ecosystem | Affected | Fixed in | | --- | --- | --- | --- | | `fast-uri` | npm | From 2.4.1 | 2.4.5 | | `fast-uri` | npm | From 2.4.1 | 2.4.5 | | `fast-uri` | npm | From 3.1.2 | 3.1.6 | | `fast-uri` | npm | From 3.1.2 | 3.1.6 | | `fast-uri` | npm | From 4.0.0 | 4.1.3 | | `fast-uri` | npm | From 4.0.0 | 4.1.3 | Products: Openjsf Fast-Uri. ## How do I fix CVE-2026-75899? Upgrade fast-uri to a fixed version for your release line: 2.4.5, 3.1.6 or 4.1.3. ## Is CVE-2026-75899 being exploited? There is no known exploitation of CVE-2026-75899 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-2026-75931](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) - [CVE-2026-76172](https://insights.sbomify.com/CVE-2026-76172/): fast-uri vulnerable to host confusion via percent-encoded scheme normalization (high 7.5) ## Fix prompt for AI coding agents ```text Check this codebase for CVE-2026-75899 and fix it if it is affected. What it is: CVE-2026-75899 is a high-severity server-side request forgery vulnerability in fast-uri, published on 24 Aug 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-2026-75899 in the wild and no public exploit code. Affected packages and fixed versions: - fast-uri (npm): affected from 2.4.1; fixed in 2.4.5 - fast-uri (npm): affected from 2.4.1; fixed in 2.4.5 - fast-uri (npm): affected from 3.1.2; fixed in 3.1.6 - fast-uri (npm): affected from 3.1.2; fixed in 3.1.6 - fast-uri (npm): affected from 4.0.0; fixed in 4.1.3 - fast-uri (npm): affected from 4.0.0; fixed in 4.1.3 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-2026-75899/ (Markdown: https://insights.sbomify.com/CVE-2026-75899/index.md) ``` ## Sources - CVE record: https://www.cve.org/CVERecord?id=CVE-2026-75899 - NVD: https://nvd.nist.gov/vuln/detail/CVE-2026-75899 - OSV: https://osv.dev/vulnerability/CVE-2026-75899 --- From sbomify Insights: https://insights.sbomify.com/CVE-2026-75899/ Summaries are generated and may contain mistakes; the official description above is the record.