CVE-2026-56386 Apache bRPC: Integer Underflow and Out-of-Bounds Read in HTTP/2 DATA Frame Parser
- Exploited in the wild
- Not known
- Fix
- None listed
What is CVE-2026-56386?
CVE-2026-56386 is a high-severity vulnerability in Apache bRPC, published on 21 Oct 2026.
Official description
Integer underflow and out-of-bounds read in the HTTP/2 server DATA frame parser in Apache bRPC allows an unauthenticated remote attacker to cause denial of service by sending a malformed DATA frame with the PADDED flag set and a zero-length payload.
Root Cause: The HTTP/2 DATA frame handler computed the fragment size from the attacker-controlled payload length and, when the PADDED flag was present, decremented the fragment size before ensuring that the frame contained the mandatory pad length byte. A zero-length padded DATA frame could therefore underflow the unsigned fragment size and read the pad length byte past the end of the frame buffer.
Affected Scenarios: Apache bRPC servers that accept HTTP/2 traffic are affected when a remote client can send crafted HTTP/2 frames to the server. HTTP/2 may be reached through cleartext h2c detection on an HTTP port or through TLS ALPN negotiation.
How to Fix: (Choose one of the following options) 1. Upgrade Apache bRPC to version 1.18.0, which fixes this issue. 2. Apply this patch: https://github.com/apache/brpc/pull/3325
Note: The fix validates that a padded DATA frame has enough payload bytes for the pad length field before decrementing the fragment size or reading the pad length byte. Malformed zero-length padded DATA frames are rejected with HTTP/2 FRAME_SIZE_ERROR.
Which versions are affected by CVE-2026-56386?
How do I fix CVE-2026-56386?
No fix has been published for CVE-2026-56386 yet. Limit exposure of the affected software until one is available.
Is CVE-2026-56386 being exploited?
There is no known exploitation of CVE-2026-56386 in the wild and no public exploit code.
Sources
Also known as GHSA-wj5x-6jj2-m348.