CVE-2026-28898 is a medium-severity (CVSS 5.3) CWE-116 vulnerability in github.com/apple/swift-nio-http2. O3 Security confirms whether CVE-2026-28898 is actually reachable in your code before you act, and blocks exploitation at runtime until you patch.
SwiftNIO HTTP/2: HTTP/2-to-HTTP/1 Request Smuggling via unvalidated :path pseudo-header in HTTP2ToHTTP1Codec
Exploitation Status
No confirmed exploitation observed yet
- CISA assesses this as automatable — exploitation doesn’t require manual, per-target effort, which raises the odds of mass scanning and opportunistic attacks.
- CISA’s own triage has not observed active exploitation or public proof-of-concept code for this CVE as of its last assessment.
Exploitation and automatability from CISA’s SSVC triage for CVE-2026-28898.
EPSS Exploitation Probability
EPSS (Exploit Prediction Scoring System) is a daily probability model maintained by FIRST.org. It estimates the likelihood a CVE will be exploited in production environments within the next 30 days, derived from real-world threat intelligence signals.
How urgent is this, really
CVE-2026-28898 plotted by exploitation likelihood (EPSS) against impact (CVSS). The shaded corner — EPSS 50%+ and CVSS 7.0+ — is where this CVE doesn't sit, though severity or exploitability alone can still warrant action.
Where this sits among everything scored
Of 371,256 CVEs with a current EPSS score, this one falls in the < 10% band (highlighted). Real counts from FIRST.org, not a sample — log-scaled since the landscape is heavily right-skewed.
Real-World Exposure
github.com/apple/swift-nio-http2Real-time download stats are indexed for npm and PyPI packages. This vulnerability affects SwiftURL packages — download data is not available via public APIs for these ecosystems.
Description
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.
Affected Packages
| Ecosystem | Package | Vulnerable range | Fix |
|---|---|---|---|
| 📦SwiftURL | github.com/apple/swift-nio-http2 | all versions | 1.44.0 |
Detection & mitigation playbook
Open-source dependencyDetect
Scan your dependency tree (package-lock.json, pnpm-lock.yaml, requirements.txt, go.sum, etc.) for github.com/apple/swift-nio-http2. O3's reachability analysis confirms whether the vulnerable code path is actually invoked in your application, so you act on real exposure instead of every transitive match.
Fix
Update github.com/apple/swift-nio-http2 to 1.44.0 or later, then make sure no transitive (indirect) dependency still pins the vulnerable range — O3 confirms CVE-2026-28898 is resolved across your whole dependency graph.
Workarounds
If you can't upgrade right away: gate or disable the affected feature, validate untrusted input at the boundary, and avoid passing attacker-controlled data into the vulnerable path. O3's runtime protection blocks exploitation in production as an interim safeguard until the upgrade lands.
How O3 protects you
O3 pinpoints whether CVE-2026-28898 is reachable in your code and exactly where to fix it, then blocks exploitation in production at runtime until the patched version is deployed.
Tailored to CVE-2026-28898. Runtime protection reduces exposure until a permanent patch is applied and verified — it complements patching, it doesn't replace it.
Frequently Asked Questions
Is CVE-2026-28898 in your dependencies?
O3 detects CVE-2026-28898 across SwiftURL dependencies and uses function-level reachability to confirm whether the vulnerable code path is actually reachable — not just present. No false positives.