CVE-2026-26962 Rack: Header injection in multipart requests
Attackers can inject headers via multipart requests in Rack, potentially causing response splitting in applications using affected versions.
- Exploited in the wild
- Not known
- Login needed
- Not needed
- Attackable
- Over the internet
- Victim action needed
- Not needed
- Fix
- Available
What is CVE-2026-26962?
CVE-2026-26962 is a medium-severity vulnerability in rack, published on 2 Apr 2026. An attacker can exploit it over the internet without logging in, with no action from the victim.
Official description
Rack is a modular Ruby web server interface. From version 3.2.0 to before version 3.2.6, Rack::Multipart::Parser unfolds folded multipart part headers incorrectly. When a multipart header contains an obs-fold sequence, Rack preserves the embedded CRLF in parsed parameter values such as filename or name instead of removing the folded line break during unfolding. As a result, applications that later reuse those parsed values in HTTP response headers may be vulnerable to downstream header injection or response splitting. This issue has been patched in version 3.2.6.
Weakness: CWE-93
Which versions are affected by CVE-2026-26962?
2 open source packages ship an affected version, including rack. It affects 1 product.
| Package | Affected | Fixed in |
|---|---|---|
rack RubyGems | From 3.2.0 | 3.2.6 |
rack RubyGems | From 3.2.0 | 3.2.6 |
Products include Rack Rack.
How do I fix CVE-2026-26962?
Upgrade rack to 3.2.6 or later.
Is CVE-2026-26962 being exploited?
There is no known exploitation of CVE-2026-26962 in the wild and no public exploit code.
Other vulnerabilities in rack
- CVE-2026-34785 Rack: Local file inclusion in `Rack::Static` via URL Prefix Matching
- CVE-2026-34827 Rack: Algorithmic-Complexity DoS in Rack::Multipart::Parser
- CVE-2026-34829 Rack: Denial of Service via Unbounded Multipart File Upload Without Content-Length
- CVE-2026-22860 Rack has a Directory Traversal via Rack:Directory
- CVE-2025-61919 Rack is vulnerable to a memory-exhaustion DoS through unbounded URL-encoded body parsing
Sources
Also known as DEBIAN-CVE-2026-26962, GHSA-rx22-g9mx-qrhv, MINI-3493-hh35-8q5w, MINI-73h8-3r33-8w27, MINI-c2wf-6545-wqvp, MINI-f7j9-m4hx-x6pc and 2 more.