GHSA-r5rp-j6wh-rvv4 is a medium-severity (CVSS 4.8) Improper Input Validation vulnerability in hono. O3 Security confirms whether GHSA-r5rp-j6wh-rvv4 is actually reachable in your code before you act, and blocks exploitation at runtime until you patch.
Hono: Non-breaking space prefix bypass in cookie name handling in getCookie()
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.
Real-World Exposure
How broadly this vulnerability is actually deployed: weekly install volume shows current usage, a proxy for how much of the ecosystem is exposed.
hononpmDescription
Summary
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.
Details
Browsers follow RFC 6265bis and only trim SP (0x20) and HTAB (0x09) from cookie names. Other characters, such as the non-breaking space (U+00A0), are preserved as part of the cookie name.
For example, the browser treats the following cookies as distinct:
"dummy-cookie"
"\u00a0dummy-cookie"
However, parse() previously used JavaScript's trim(), which removes a broader set of characters including U+00A0. As a result, both names are normalized to:
"dummy-cookie"
This mismatch allows attacker-controlled cookies with a U+00A0 prefix to shadow or override legitimate cookies when accessed via getCookie().
Impact
An attacker who can set cookies (e.g., via a man-in-the-middle on a non-secure page or other injection vector) can bypass cookie prefix protections and override sensitive cookies.
This may lead to:
- Bypassing
__Secure-and__Host-prefix protections - Overriding cookies that rely on the Secure attribute
- Session fixation or session hijacking depending on application usage
This issue affects applications that rely on getCookie() for security-sensitive cookie handling.
Affected Packages
| Ecosystem | Package | Vulnerable range | Fix |
|---|---|---|---|
| 📦npm | hono | all versions | 4.12.12 |
Detection & mitigation playbook
Open-source dependencyDetect
Scan your dependency tree (package-lock.json, pnpm-lock.yaml, requirements.txt, go.sum, etc.) for hono. 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 hono to 4.12.12 or later, then make sure no transitive (indirect) dependency still pins the vulnerable range — O3 confirms GHSA-r5rp-j6wh-rvv4 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 GHSA-r5rp-j6wh-rvv4 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 GHSA-r5rp-j6wh-rvv4. Runtime protection reduces exposure until a permanent patch is applied and verified — it complements patching, it doesn't replace it.
Frequently Asked Questions
Is GHSA-r5rp-j6wh-rvv4 in your dependencies?
O3 detects GHSA-r5rp-j6wh-rvv4 across npm dependencies and uses function-level reachability to confirm whether the vulnerable code path is actually reachable — not just present. No false positives.