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CVE-2026-28898 is a low severity vulnerability with a CVSS score of 0.0. No known exploits currently, and patches are available.
Very low probability of exploitation
EPSS predicts the probability of exploitation in the next 30 days based on real-world threat data, complementing CVSS severity scores with actual risk assessment.
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.
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