CVE-2026-29085

Hono: SSE Control Field Injection via CR/LF in writeSSE()

CVSS 3.1 6.5 MEDIUMEUVD CVSS 3.1 6.5 CVSS 3.1 · [email protected] · Secondary 6.5 MEDIUMCVSS_V3 Publisher rating MODERATEFixed by hono 4.12.4KEV status unknown

Original advisory

cve-program · CVE-2026-29085

Published

Hono is a Web application framework that provides support for any JavaScript runtime. Prior to version 4.12.4, when using streamSSE() in Streaming Helper, the event, id, and retry fields were not validated for carriage return (\r) or newline (\n) characters. Because the SSE protocol uses line breaks as field delimiters, this could allow injection of additional SSE fields within the same event frame if untrusted input was passed into these fields. This issue has been patched in version 4.12.4.

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euvd · EUVD-2026-9507

Published

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nvd · CVE-2026-29085

Published

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osv · GHSA-p6xx-57qc-3wxr

Published

## Summary When using `streamSSE()` in Streaming Helper, the `event`, `id`, and `retry` fields were not validated for carriage return (`\r`) or newline (`\n`) characters. Because the SSE protocol uses line breaks as field delimiters, this could allow injection of additional SSE fields within the same event frame if untrusted input was passed into these fields. ## Details The SSE helper builds event frames by joining lines with `\n`. While multi-line `data:` fields are handled according to the SSE specification, the `event`, `id`, and `retry` fields previously allowed raw values without rejecting embedded CR/LF characters. Including CR/LF in these control fields could allow unintended additional fields (such as `data:`, `id:`, or `retry:`) to be injected into the event stream. The issue has been fixed by rejecting CR/LF characters in these fields. ## Impact An attacker could manipulate the structure of SSE event frames if an application passed user-controlled input directly into `event`, `id`, or `retry`. Depending on application behavior, this could result in injected SSE fields or altered event stream handling. Applications that render `e.data` in an unsafe manner (for example, using `innerHTML`) could potentially expose themselves to client-side script injection. This issue affects applications that rely on the SSE helper to enforce protocol-level constraints.

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Affected versions, risk and source history

Exploitation and risk

Source status

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Risk history

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Advisory history

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15 Nov 2026 12:01:23 UTC