Yamux Memory Exhaustion Vulnerability via Active::pending_frames propertyGHSA-3999-5ffv-wp2r
HIGHFix: libp2p/rust-yamux@460baf2GHSA-3999-5ffv-wp2r is a high-severity (CVSS 7.5) Uncontrolled Resource Consumption vulnerability in yamux. A fix is available for yamux — see the affected versions and patch details below.
Exploitation Status
No confirmed exploitation observed yet
- CISA assesses this as automatable — exploitation doesn’t require manual, per-target effort, which raises the odds of mass scanning and opportunistic attacks.
- CISA’s own triage has not observed active exploitation or public proof-of-concept code for this CVE as of its last assessment.
Exploitation and automatability from CISA’s SSVC triage for GHSA-3999-5ffv-wp2r.
EPSS Exploitation Probability
Probability of exploitation in the next 30 days, from FIRST.org EPSS.
How urgent is this, really
Where this sits among everything scored
Real-World Exposure
yamuxReal-time download stats are indexed for npm and PyPI packages. This vulnerability affects crates.io packages — download data is not available via public APIs for these ecosystems.
Description
Summary
Attack scenario The Rust implementation of the Yamux stream multiplexer uses a vector for pending frames. This vector is not bounded in length. Every time the Yamux protocol requires sending of a new frame, this frame gets appended to this vector. This can be remotely triggered in a number of ways, for example by:
- Opening a new libp2p Identify stream. This causes the node to send its Identify message. Of course, every other protocol that causes the sending of data also works. The larger the response, the more data is enqueued.
- Sending a Yamux Ping frame. This causes a Pong frame to be enqueued.
Under normal circumstances, this queue of pending frames would be drained once they’re sent out over the network. However, the attacker can use TCP’s receive window mechanism to prevent the victim from sending out any data: By not reading from the TCP connection, the receive window will never be increased, and the victim won’t be able to send out any new data (this is how TCP implements backpressure). Once this happens, Yamux’s queue of pending frames will start growing indefinitely. The queue will only be drained once the underlying TCP connection is closed.
Components https://github.com/libp2p/rust-yamux/blob/yamux-v0.13.1/yamux/src/connection.rs#L289
Details
This attack is inspired by the HTTP/2 Rapid Reset Attack (CVE 2023-44487), HTTP/2 Ping Flood (CVE-2019-9512), and the QUIC Path Validation attack (see my blog post: https://seemann.io/posts/2023-12-18-exploiting-quics-path-validation/).
Impact
An attacker can cause a remote node to run out of memory, which will result in the corresponding process getting terminated by the operating system.
Depending on the application protocols running on top of rust-libp2p, higher amplification factors are possible. For example, image a protocol that sends out 10 MB of data as a result of an incoming request. By issuing that request and sending a Yamux stream window update (together ~100-200 bytes), the victim would now enqueue the entire 10 MB into its frame buffer. Any block transfer / sync protocols might be good candidates.
In addition to consuming huge amounts of memory, this attack also drives up the victim's CPU load, such that the allocation of memory at some point becomes CPU-limited.
This was originally submitted by @marteen-seemann to the Ethereum Foundation bug bounty program.
Affected Packages
| Ecosystem | Package | Vulnerable range | Fix |
|---|---|---|---|
| 🦀crates.io | yamux | ≥ 0.13.0&&< 0.13.2 | 0.13.2cargo update -p yamux --precise 0.13.2 |
Detection & mitigation playbook
Open-source dependencyDetect
Scan your dependency tree (package-lock.json, pnpm-lock.yaml, requirements.txt, go.sum, etc.) for yamux, including transitive dependencies — a direct dependency you never call can still pull in a vulnerable version.
Fix
Update yamux to 0.13.2 or later, then make sure no transitive (indirect) dependency still pins the vulnerable range — O3 confirms GHSA-3999-5ffv-wp2r is resolved across your whole dependency graph.
Workarounds
Cap what an attacker can consume: apply request size, rate and timeout limits in front of the affected component, and run it with memory and CPU limits so exhaustion degrades one worker rather than the whole service.
Frequently Asked Questions
Is GHSA-3999-5ffv-wp2r in your dependencies?
Find it across crates.io, including transitive dependencies.