GHSA-84xm-r438-86px

Описание

Note: This vulnerability was originally reported to the Google OSS VRP (Issue ID: 477542544). The Google Security Team requested that I coordinate directly with the Envoy maintainers for triage and remediation. I am submitting this report here to facilitate that process.

Technical Details I have identified a logic vulnerability in Envoy's HTTP connection manager (FilterManager) that allows for Zombie Stream Filter Execution. This issue creates a "Use-After-Free" (UAF) or state-corruption window where filter callbacks are invoked on an HTTP stream that has already been logically reset and cleaned up.

Mechanism: The vulnerability resides in source/common/http/filter_manager.cc within the FilterManager::decodeData method.

When an HTTP/2 stream encounters a reset condition (e.g., StreamIdleTimeout, OverloadManager limits, or a local reset triggered by a filter), Envoy calls onResetStream. This method:

1. Sets the internal state state_.saw_downstream_reset_ = true.
2. Invokes onDestroy() on all filters in the chain (allowing them to release resources/pointers).
3. Schedules the ActiveStream object for deferred deletion (cleanup happens later in the event loop).

The Flaw: The ActiveStream object remains valid in memory during the deferred deletion window. If a DATA frame arrives on this stream immediately after the reset (e.g., in the same packet processing cycle), the HTTP/2 codec invokes ActiveStream::decodeData, which cascades to FilterManager::decodeData.

FilterManager::decodeData fails to check the saw_downstream_reset_ flag. It iterates over the decoder_filters_ list and invokes decodeData() on filters that have already received onDestroy().

Root Cause Code Location: File: source/common/http/filter_manager.cc Function: FilterManager::decodeData

Suggested Fix: Add an explicit state check at the beginning of FilterManager::decodeData.

Impact Analysis

Who can exploit this: Any remote attacker capable of establishing an HTTP/2 or HTTP/3 connection. No privileges/authentication required.

Impact & Gain: 1. Memory Corruption & Potential Remote Code Execution: While the immediate symptom is a crash (DoS), the underlying primitive is a Use-After-Free (CWE-416).

• Mechanism: When onDestroy() is called on filters (e.g., Lua, Wasm, or complex native filters), they release internal structures and invalidate pointers.
• Exploitation: By forcing decodeData() to execute on these now-freed objects, an attacker triggers undefined behavior. In a heap-groomed environment, an attacker could potentially replace the freed filter object with a malicious payload before the "Zombie" decodeData call occurs. This would allow for vtable hijacking or arbitrary write-what-where primitives, leading to Remote Code Execution (RCE).
• Risk Amplification: This is particularly dangerous for Envoy deployments using memory-unsafe extensions or third-party filters (C++ extensions), where onDestroy logic is relied upon for safety.

2. Security Control Bypass: The vulnerability defeats Envoy's "Fail-Closed" security architecture.

• Scenario: If a stream is reset due to a security violation (e.g., StreamIdleTimeout, OverloadManager rejection, or WAF triggering), this vulnerability allows the attacker to bypass the termination.
• Result: The attacker can force the processing of "Data" frames on a connection that the security policy explicitly attempted to close, allowing malicious payloads to reach deeper into the filter chain or backend services despite the rejection.

Proof of Concept (Unit Test)

Description: The attached C++ unit test (zombie_stream_poc_test.cc) deterministically reproduces the vulnerability. It creates a stream, manually triggers a reset (simulating an Overload), and then immediately injects a DATA frame. The test asserts that the filter's decodeData callback is invoked on the reset stream.