CVE-2026-44909 in Proxygen
Summary
by MITRE • 07/23/2026
Proxygen lacked a generalized slow-consumer detection mechanism in its core HTTP session layer. A remote, unauthenticated attacker could exploit HTTP/2 flow-control by setting SETTINGS_INITIAL_WINDOW_SIZE to 0 or withholding WINDOW_UPDATE frames, causing the server to buffer complete response bodies in memory indefinitely for stalled streams. By opening many simultaneous streams requesting large resources while preventing the server from transmitting responses, an attacker could induce unbounded memory growth leading to service degradation, resource exhaustion, or denial of service. Versions v2017.01.16.00 through v2026.07.20.00 are affected.
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Analysis
by VulDB Data Team • 07/23/2026
The vulnerability in Proxygen represents a critical design flaw in the HTTP session layer that fundamentally undermines the server's ability to manage resource consumption effectively. This weakness stems from the absence of a generalized slow-consumer detection mechanism, which is essential for maintaining system stability under adverse network conditions. The flaw specifically targets the HTTP/2 flow-control implementation where the protocol's window management system becomes exploitable when attackers manipulate core connection parameters. The vulnerability manifests through manipulation of SETTINGS_INITIAL_WINDOW_SIZE parameter set to zero or by strategically withholding WINDOW_UPDATE frames, creating a condition where the server continuously buffers complete response bodies in memory without any mechanism to detect or terminate these stalled streams.
The technical exploitation of this vulnerability follows a systematic approach that leverages fundamental HTTP/2 protocol behaviors to achieve resource exhaustion. Attackers can establish multiple simultaneous streams while requesting large resources, effectively creating a scenario where each stream remains in a stalled state due to the manipulated flow-control parameters. The server's response handling mechanism becomes overwhelmed as it attempts to buffer complete response bodies for these indefinitely stalled streams, leading to unbounded memory consumption that grows linearly with each active stream. This design deficiency creates an ideal environment for denial-of-service attacks where resource exhaustion occurs without requiring authentication or sophisticated attack vectors, making the vulnerability particularly dangerous in production environments.
The operational impact of this vulnerability extends far beyond simple service disruption, creating cascading effects that can compromise entire system availability and performance. When memory consumption grows indefinitely due to buffered response bodies, the server experiences significant degradation in performance characteristics, eventually leading to complete service unavailability. The resource exhaustion affects not only memory but also CPU utilization as the system attempts to process these stalled streams, potentially causing additional system instability. This vulnerability is particularly concerning because it can be exploited by remote attackers without authentication, meaning that any accessible Proxygen-based service becomes immediately vulnerable to exploitation. The attack surface includes web servers, API gateways, and any application utilizing Proxygen's HTTP session handling capabilities, making it a widespread concern across organizations relying on this software stack.
Mitigation strategies for this vulnerability must address both the immediate exposure and implement long-term architectural improvements to prevent similar issues in future implementations. The most effective approach involves implementing proper slow-consumer detection mechanisms that can identify and terminate stalled streams before they consume excessive resources. Organizations should consider patching affected versions of Proxygen, with the vulnerable range spanning from v2017.01.16.00 through v2026.07.20.00, though the specific mitigation timeline depends on deployment schedules and risk tolerance. Network-level protections such as connection limiting and rate limiting can provide additional defense-in-depth measures to reduce the impact of exploitation attempts. Implementing monitoring solutions that track memory consumption patterns and stream states can help detect exploitation attempts before they cause significant damage. From a security framework perspective, this vulnerability aligns with CWE-400 weakness category for unspecified resource exhaustion and relates to ATT&CK technique T1499.004 for network disruption through resource exhaustion attacks. The mitigation approach should also consider implementing automated stream cleanup mechanisms that can detect and close streams exceeding predetermined time or memory thresholds, providing a robust defense against this specific class of attack vectors.