CVE-2026-86147 Vulnerability Analysis & Exploit Details

CVE-2026-86147 Vulnerability Summary

CVE-2026-86147: External control of file name or path and uncontrolled resource consumption in Apache bRPC (version < 1.18.0) on all platforms allows remote attackers who can reach the builtin service port to create directories and truncate/overwrite files with the privileges of the server process, or to hold the process-wide CPU/contention profiler for an arbitrarily long time. Root Cause: 1. The builtin /flags service allows gflags carrying a validator to be modified at runtime via ?setvalue=. The bvar/mbvar dump path gflags (bvar_dump_file, bvar_dump_tabs, mbvar_dump_file) were registered with an accept-anything validator whose only purpose was to wake the dumping thread. A remote attacker could therefore repoint the dump path (e.g. GET /flags/bvar_dump_file?setvalue=/victim/dir/target followed by GET /flags/bvar_dump?setvalue=true, or the equivalent for mbvar_dump_file, which is used verbatim without a forced suffix), making the dumping thread recursively create directories and open/truncate files at attacker-chosen locations. Tab names in bvar_dump_tabs were appended to the path without sanitization, allowing '..' to escape the configured directory. 2. The /pprof builtin service did not clamp the ?seconds= parameter to FLAGS_max_profiling_seconds (a limit that /hotspots enforced). A single request such as ?seconds=2147483647 made the handler sleep for decades while holding the process-wide gperftools CPU profiler or bthread contention profiler, so /hotspots/cpu and /hotspots/contention returned 503 for everyone else during that time. Affected Scenarios: Any Apache bRPC server exposing the builtin services (enabled by default on the same port as normal RPC traffic) to untrusted networks. How to Fix: (Choose one of the following options) 1. Upgrade bRPC to version 1.18.0, which fixes this issue. 2. Apply this patch: https://github.com/apache/brpc/pull/3523 Note: After the fix, bvar_dump_file, bvar_dump_tabs and mbvar_dump_file can no longer be modified at runtime through the /flags builtin service. They can still be changed programmatically via google::SetCommandLineOption(), taking effect on the next dump cycle. The profiling duration of /pprof is now capped by the -max_profiling_seconds gflag (default 300 seconds), which can be adjusted by the server owner.

CVE-2026-86147 References

External References

• https://lists.apache.org/thread/2pf15ojj0vr7rtx95677kgtl1mx3gdgb

CWE Common Weakness Enumeration

CAPEC Common Attack Pattern Enumeration and Classification

• XML Ping of the Death CAPEC-147 An attacker initiates a resource depletion attack where a large number of small XML messages are delivered at a sufficiently rapid rate to cause a denial of service or crash of the target. Transactions such as repetitive SOAP transactions can deplete resources faster than a simple flooding attack because of the additional resources used by the SOAP protocol and the resources necessary to process SOAP messages. The transactions used are immaterial as long as they cause resource utilization on the target. In other words, this is a normal flooding attack augmented by using messages that will require extra processing on the target.
• Sustained Client Engagement CAPEC-227 An adversary attempts to deny legitimate users access to a resource by continually engaging a specific resource in an attempt to keep the resource tied up as long as possible. The adversary's primary goal is not to crash or flood the target, which would alert defenders; rather it is to repeatedly perform actions or abuse algorithmic flaws such that a given resource is tied up and not available to a legitimate user. By carefully crafting a requests that keep the resource engaged through what is seemingly benign requests, legitimate users are limited or completely denied access to the resource.
• Regular Expression Exponential Blowup CAPEC-492 An adversary may execute an attack on a program that uses a poor Regular Expression(Regex) implementation by choosing input that results in an extreme situation for the Regex. A typical extreme situation operates at exponential time compared to the input size. This is due to most implementations using a Nondeterministic Finite Automaton(NFA) state machine to be built by the Regex algorithm since NFA allows backtracking and thus more complex regular expressions.

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