CVE-2026-81755: Apache bRPC: Uncontrolled Resource Consumption via Excessive Streams in a Single RPC Request
Uncontrolled resource consumption in the streaming RPC component of Apache bRPC (version < 1.18.0) allows a remote attacker to exhaust server memory and cause denial of service by sending a single RPC request that declares an excessive number of streams.
Root Cause: In the streaming RPC feature, a client can declare multiple streams in one RPC request by putting extra stream identifiers into the repeated field streamsettings.extrastreamids of the RPC meta. On the server side, StreamAccept creates one response stream for every stream identifier declared by the request, without limiting the number of streams accepted in a single RPC. The request body size is only bounded by maxbodysize (default 64MB), which is enough to carry millions of stream identifiers. Each accepted stream allocates its own bthread execution queue and associated resources, so a single crafted request can make the server create a huge number of streams and exhaust memory, leading to denial of service.
Affected Scenarios: Use a bRPC server that serves streaming RPC and calls StreamAccept to accept streams from untrusted clients.
How to Fix: (Choose one of the following options) 1. Upgrade bRPC to the 1.18.0 version. 2. Apply this patch: https://github.com/apache/brpc/pull/3493
Note: The fix adds a new gflag streammaxstreamsperrequest with a default value of 64. Requests declaring more streams than the limit are rejected before any response stream is created. Applications that legitimately need to accept more than 64 streams in one RPC must raise this flag; otherwise such requests will fail after applying the fix.
Affected Software
Remediation
Recommended actions to resolve this vulnerability, in priority order.
- Upgrade
Upgrade
Apache bRPCto a version that resolves this vulnerability.Fixed in 1.18.0 - Configuration
For applications that legitimately need to accept more than 64 streams in one RPC, raise stream_max_streams_per_request above its default value of 64.
Apache bRPC stream_max_streams_per_request = greater than 64
Event History
Frequently Asked Questions
Which deployments are exposed?
Deployments are exposed when they use a bRPC server with streaming RPC enabled and call StreamAccept to accept streams from untrusted clients. Versions earlier than 1.18.0 are affected.
What does an attacker need to exploit this?
An attacker needs to be able to send a crafted streaming RPC request to the server. The request declares many stream identifiers in stream_settings.extra_stream_ids, causing the server to create a response stream and associated resources for each one.
Does the default request-size limit prevent exploitation?
No. The default max_body_size is 64 MB, which is sufficient to carry millions of stream identifiers, so a single request can exhaust server memory.
How can I identify potentially vulnerable application paths?
Review streaming RPC handlers for calls to StreamAccept that accept streams from untrusted clients. Those paths are susceptible if they run on a bRPC version earlier than 1.18.0.