Summary
SwiftNIO HTTP/2: HTTP/2-to-HTTP/1 Request Smuggling via unvalidated :path pseudo-header in HTTP2ToHTTP1Codec
swift-nio-http2's HTTP/2-to-HTTP/1.1 codec (HTTP2FramePayloadToHTTP1ServerCodec / HTTP2ToHTTP1ServerCodec) did not validate pseudo-header values for control characters before placing them into the translated HTTP/1.1 message. A remote attacker could send an HTTP/2 request containing CR (\r), LF (\n), or NUL (\0) bytes in pseudo-header values such as :path, and when the server translated this to HTTP/1.1, for example in a reverse-proxy configuration, the resulting output could contain injected headers or entirely smuggled requests.
This is an HTTP/2-to-HTTP/1.1 request smuggling vulnerability. HTTP/2's binary framing means that CRLF bytes are never parsed as line terminators at the HTTP/2 layer, so they pass through transparently to the HTTP/1.1 output. Any swift-nio-http2 server that translates HTTP/2 requests to HTTP/1.1 and forwards them to a backend is affected. Server-side Swift frameworks such as Vapor that use this codec in a reverse-proxy pattern are directly affected.
This vulnerability is related to https://github.com/advisories/GHSA-7fj7-39wj-c64f in swift-nio, which addressed CRLF injection in HTTP/1.1 header values but did not cover pseudo-header values in the HTTP/2 layer.
This vulnerability is also related to https://github.com/advisories/GHSA-cq87-8r7h-962v in swift-nio, which addressed CRLF injection in HTTP/1.1 version, method and path.
swift-nio-http2 1.44.0 adds validation of all pseudo-header values (:path, :authority, :scheme, :method, and :status) at both the HPACK header validation layer and the HTTP/2-to-HTTP/1.1 translation layer. Requests or responses containing CR, LF, or NUL bytes in any pseudo-header value are now rejected with a connection error.
SwiftNIO recommends all adopters upgrade to 1.44.0 as soon as possible.
SwiftNIO thanks @kuranikaran for filing this issue and the support in fixing it.
Impact
Affected versions
Security releases
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Frequently Asked Questions
- What is CVE-2026-28898? CVE-2026-28898 is a low-severity security vulnerability in github.com/apple/swift-nio-http2 (swift), affecting versions < 1.44.1. It is fixed in 1.44.1.
- Which versions of github.com/apple/swift-nio-http2 are affected by CVE-2026-28898? github.com/apple/swift-nio-http2 (swift) versions < 1.44.1 is affected.
- Is there a fix for CVE-2026-28898? Yes. CVE-2026-28898 is fixed in 1.44.1. Upgrade to this version or later.
- Is CVE-2026-28898 exploitable, and should I be worried? Whether CVE-2026-28898 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-2026-28898 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-2026-28898? Upgrade
github.com/apple/swift-nio-http2to 1.44.1 or later.