What’s Vulnerable › Vulnerabilities

CVE-2026-39410: Hono has a non-breaking space prefix bypass in cookie name handling in getCookie()

• Severity: medium (CVSS 4.8 v3.1)
• Exploited in the wild: not listed in CISA KEV
• EPSS: 0.3% probability of exploitation in the next 30 days
• Public exploit or detection template: none known
• Published: 2026-04-08 · updated 2026-07-24
• Weakness: CWE-20

Description

Hono is a Web application framework that provides support for any JavaScript runtime. Prior to 4.12.12, a discrepancy between browser cookie parsing and parse() handling allows cookie prefix protections to be bypassed. Cookie names that are treated as distinct by the browser may be normalized to the same key by parse(), allowing attacker-controlled cookies to override legitimate ones. This vulnerability is fixed in 4.12.12.

Affected products

• honojs hono: through 4.12.11

References

• https://github.com/honojs/hono/commit/cc067c85592415cb1880ad3c61ed923472452ec0
• https://github.com/honojs/hono/releases/tag/v4.12.12
• https://github.com/honojs/hono/security/advisories/GHSA-r5rp-j6wh-rvv4

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