CVE-2019-9517

CVE-2019-9517 is a high-severity vulnerability in Apple Swiftnio with a CVSS 3.x base score of 7.5. Its EPSS exploit-prediction score of 27% places it in the 98th percentile, indicating an elevated likelihood of exploitation. The underlying weakness is classified as CWE-770.

Key facts

Description

Some HTTP/2 implementations are vulnerable to unconstrained interal data buffering, potentially leading to a denial of service. The attacker opens the HTTP/2 window so the peer can send without constraint; however, they leave the TCP window closed so the peer cannot actually write (many of) the bytes on the wire. The attacker then sends a stream of requests for a large response object. Depending on how the servers queue the responses, this can consume excess memory, CPU, or both.

Frequently asked questions

What is CVE-2019-9517?
Some HTTP/2 implementations are vulnerable to unconstrained interal data buffering, potentially leading to a denial of service. The attacker opens the HTTP/2 window so the peer can send without constraint; however, they leave the TCP window closed so the peer cannot actually write (many of) the bytes on the wire. The attacker then sends a stream of requests for a large response object. Depending on how the servers queue the responses, this can consume excess memory, CPU, or both.
How severe is CVE-2019-9517?
CVE-2019-9517 has a CVSS 3.x base score of 7.5, rated high severity. It is exploitable over network with low attack complexity, requires no privileges and no user interaction. Impact on confidentiality is none, integrity none, and availability high.
Is CVE-2019-9517 being actively exploited?
It is not currently listed in CISA's KEV catalog. Its EPSS exploit-prediction score is 27% (98th percentile), an estimate of the probability of exploitation in the next 30 days.
What products are affected by CVE-2019-9517?
CVE-2019-9517 primarily affects Apple Swiftnio. In total, 33 product configurations (CPEs) are listed as vulnerable; see the affected-products list for the exact versions.
How do I fix CVE-2019-9517?
Review the linked vendor and NVD advisories for patched versions and mitigations, then upgrade or apply the recommended workaround. Given its high severity, prioritise patching exposed systems.
When was CVE-2019-9517 published?
CVE-2019-9517 was published on 2019-08-13 and last updated on 2026-06-17.

References

Affected products (33)

More vulnerabilities in Apple Swiftnio

All CVEs affecting Apple Swiftnio →

Other CWE-770 (Allocation of Resources Without Limits or Throttling) vulnerabilities

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Threat intelligence

Threat-intel indicators referencing this CVE: