CVE-2021-29991

What it actually does

Incorrect acceptance of a newline character in an HTTP/3 header causes the client to interpret it as two separate headers, enabling header splitting attacks against servers.

Why it matters to the business

Attackers can manipulate header processing in affected client software, potentially leading to unauthorized actions, security control bypasses, or altered server behavior during web communications; the issue affects a widely used open-source education platform with many downstream installations.

How an attack unfolds

An attacker positions a vulnerable client to receive an HTTP/3 response containing a newline within a header field; the client splits the header, allowing injected directives to reach the server and perform actions such as cache poisoning or request smuggling.

How to fix it

Update francoisjacquet/rosariosis to the fixed commit fad593be603afc7f25deff407caaaab8cbdd3bdf; verify the change is present before deployment.

How to confirm the fix worked

Confirm the exact commit hash is deployed, then test HTTP/3 responses containing embedded newlines to ensure they are rejected or normalized.

Typical attack path

1. Position vulnerable client to fetch resource over HTTP/3
2. Craft server response embedding newline inside a header value
3. Trigger client-side header splitting on newline
4. Leverage resulting split to inject malicious headers against target server

How to detect it

Review web server and client logs for HTTP/3 responses containing literal newline characters within header fields; correlate with any resulting abnormal server behavior or injected headers.

What your security team should do

• Apply the listed commit immediately due to the high CVSS score
• Scan all instances of the affected package for the vulnerable code pattern
• Monitor HTTP/3 traffic for anomalous header structures