Summary
Hackney has CR/LF injection in query parameter
hackney_url:make_url/3 passes the URL query component directly into the HTTP/1.1 request target without percent-encoding \r or \n. RFC 3986 §3.4 requires characters outside the query grammar to be percent-encoded, but no validation or escaping occurs. An attacker who controls any portion of the URL passed to hackney can inject raw CRLF sequences into the request line, enabling HTTP header injection or full request splitting.
Details
hackney_url:make_url/3 in src/hackney_url.erl builds the request target by concatenating the path and query binaries. The query string is used as-is, no character-class check, no percent-encoding of \r or \n. When hackney serializes the request, the query value lands verbatim in the GET <path>?<query> HTTP/1.1\r\n request line. A query value containing \r\n terminates the request line early; subsequent bytes are parsed by the server (or any intermediary proxy) as additional header lines or a second request.
A concrete example: a URL with query ?q=x HTTP/1.1\r\nX-Injected: yes\r\nX: produces the following on the wire:
GET /?q=x HTTP/1.1
X-Injected: yes
X: HTTP/1.1
Host: ...
The server sees X-Injected: yes as a legitimate request header that the client never intended to send.
PoC
- Listen on a raw TCP port:
nc -lvnp 8080. - Issue:
:hackney.get("http://127.0.0.1:8080/?q=x HTTP/1.1\r\nX-Injected: yes\r\nX:"). - Observe the listener receives
X-Injected: yesas a standalone header line in the request.
Resources
Impact
HTTP header injection and request splitting against any server hackney connects to. Affects all released versions of hackney before 4.0.1. Exploitation requires an attacker-controlled URL (or URL component) to reach hackney without prior sanitization. Consequences include injecting arbitrary headers (Authorization, Host, X-Forwarded-For) and splitting requests through proxies. CVSS v4.0: 6.8 (MEDIUM).
Affected versions
Security releases
Kodem intelligence
Severity tells you how bad this could be in the worst case. It does not tell you whether you are exposed. Exploitability and impact are functions of runtime truth: whether the vulnerable code is present, reachable, and actually executes in your application. A vulnerable package can sit in your dependency tree and never run.
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Frequently Asked Questions
- What is CVE-2026-47075? CVE-2026-47075 is a medium-severity security vulnerability in hackney (erlang), affecting versions < 4.0.1. It is fixed in 4.0.1.
- Which versions of hackney are affected by CVE-2026-47075? hackney (erlang) versions < 4.0.1 is affected.
- Is there a fix for CVE-2026-47075? Yes. CVE-2026-47075 is fixed in 4.0.1. Upgrade to this version or later.
- Is CVE-2026-47075 exploitable, and should I be worried? Whether CVE-2026-47075 is exploitable in your environment depends on whether the vulnerable code is present and reachable. A CVSS score is a worst-case rating; it does not account for your specific deployment, configuration, or usage patterns. Kodem, an Intelligent Application Security platform, uses runtime intelligence to show which vulnerabilities actually execute in production, so you can focus on the ones that represent real risk. Get a demo
- What actually determines whether CVE-2026-47075 is exploitable, and how bad it is? Exploitability and impact are not fixed properties of a CVE. They depend on runtime truth: whether the vulnerable code is present, reachable, and actually executes in your application. A high CVSS score on a dependency that never runs is not the same as real risk. Kodem, an Intelligent Application Security platform, uses runtime intelligence to reveal which vulnerabilities actually execute in production, so teams prioritize the ones that genuinely matter.
- How do I fix CVE-2026-47075? Upgrade
hackneyto 4.0.1 or later.