CVE-2026-78659
When "Trailer" headers are sent by a client, the HTTP server internally uses the header values to…
- Risk score
- 59/100
- CVSS
- 7.5 v3.1
- Exploit chance (30 days)
- 0.6%
- Published
- 8 Oct 2026
Open in the live forecast Today's forecast
What to know
- What it is
- When "Trailer" headers are sent by a client, the HTTP server internally uses the header values to populate the Request.Trailer map passed to the server handler. Because Request.Trailer is a map, each entry incurs memory overhead. For HTTP/2 servers, a malicious client can exploit this by sending a "Trailer" header tha…
- Affected
- See advisory
- Fix
- Apply the vendor's security update; see the linked advisory.
- Exploitation
- No known exploitation
Why it is Yellow
- CVSS 7.5 high
- Remotely exploitable without logging in
References
Original description
When "Trailer" headers are sent by a client, the HTTP server internally uses the header values to populate the Request.Trailer map passed to the server handler. Because Request.Trailer is a map, each entry incurs memory overhead. For HTTP/2 servers, a malicious client can exploit this by sending a "Trailer" header that declares a large number of fields, causing the server to allocate a disproportionate amount of memory while bypassing Server.MaxHeaderValueCount and Server.MaxHeaderBytes limits. This exploit is not applicable for HTTP/1 servers, which do not support multiplexing a large number of requests over one TCP connection, and whose Server.MaxHeaderBytes are calculated differently.
Last activity 8 Oct 2026. Patch Forecast updates every hour.