How severe is CVE-2019-8849?

CVE-2019-8849 has a CVSS score of 9.8/10, rated CRITICAL. Immediate patching is strongly recommended.

Which packages are affected by CVE-2019-8849?

CVE-2019-8849 affects the following packages: github.com/apple/swift-nio-ssl (SwiftURL). Ecosystems affected: SwiftURL.

How do I fix CVE-2019-8849?

Update github.com/apple/swift-nio-ssl to 2.4.1 or later, then make sure no transitive (indirect) dependency still pins the vulnerable range — O3 confirms CVE-2019-8849 is resolved across your whole dependency graph.

How do I detect CVE-2019-8849 in my SwiftURL dependencies?

Scan your dependency tree (package-lock.json, pnpm-lock.yaml, requirements.txt, go.sum, etc.) for github.com/apple/swift-nio-ssl, including transitive dependencies — a direct dependency you never call can still pull in a vulnerable version.

How do I mitigate CVE-2019-8849 if there is no patch (or I can't update yet)?

If you can't upgrade right away: gate or disable the affected feature, validate untrusted input at the boundary, and avoid passing attacker-controlled data into the vulnerable path. O3's runtime protection blocks exploitation in production as an interim safeguard until the upgrade lands.

How does O3 Security protect against CVE-2019-8849?

O3 Security's impact-aware SCA analyses which vulnerable code paths your application actually calls, so a match like CVE-2019-8849 can be triaged on real exposure rather than presence alone.

Is CVE-2019-8849 actively exploited in the wild?

No public exploit code has been indexed for CVE-2019-8849 yet. This does not mean the vulnerability cannot be exploited — absence of public exploits does not imply safety. Apply the recommended fix and use O3 Security to monitor your exposure.

What is the EPSS score for CVE-2019-8849?

CVE-2019-8849 has an EPSS (Exploit Prediction Scoring System) score of 2.2%, placing it in the 82th percentile of all CVEs. EPSS is maintained by FIRST.org and estimates the probability that a vulnerability will be exploited in the wild within the next 30 days. This score indicates relatively lower exploitation probability, though the CVSS severity should still guide your patching priority.

When was CVE-2019-8849 published, and has it been updated?

CVE-2019-8849 was published on December 18, 2019 and was last updated on August 7, 2026. Advisory data evolves as severity scores, affected ranges, and exploit intelligence are revised — always check the latest version of the advisory before acting.

📦

📦 SwiftURL

Not in CISA KEV

CRITICAL severity

CVE-2019-8849 — swift-nio-ssl

CRITICAL

CVE-2019-8849 is a critical-severity (CVSS 9.8) remote code execution vulnerability in github.com/apple/swift-nio-ssl. A fix is available for github.com/apple/swift-nio-ssl — see the affected versions and patch details below.

SwiftNIO SSL arbitrary code execution vulnerability

Also known asGHSA-frg3-gpcx-968f

Published

Dec 18, 2019

Updated

Aug 7, 2026

Affected

1 pkg

Patched

1 / 1

Exploits

None indexed

Exploitation data as of Sep 19, 2026 · OSV.dev, NVD, FIRST.org (EPSS)

EPSS Exploitation Probability

via FIRST.org ↗

2.2%probability of exploitation in next 30 days

Lower Risk0.00%

Lower risk than most CVEs82th percentile — riskier than 82% of all scored CVEsHighest risk

EPSS (Exploit Prediction Scoring System) is a daily probability model maintained by FIRST.org. It estimates the likelihood a CVE will be exploited in production environments within the next 30 days, derived from real-world threat intelligence signals.

How urgent is this, really

CVE-2019-8849 plotted by exploitation likelihood (EPSS) against impact (CVSS). The shaded corner — EPSS 50%+ and CVSS 7.0+ — is where this CVE doesn't sit, though severity or exploitability alone can still warrant action.

Where this sits among everything scored

Of 377,166 CVEs with a current EPSS score, this one falls in the < 10% band (highlighted). Real counts from FIRST.org, not a sample — log-scaled since the landscape is heavily right-skewed.

Real-World Exposure

1 pkg affected

📦github.com/apple/swift-nio-ssl

Real-time download stats are indexed for npm and PyPI packages. This vulnerability affects SwiftURL packages — download data is not available via public APIs for these ecosystems.

Description

The issue was addressed by signaling that an executable stack is not required. This issue is fixed in SwiftNIO SSL 2.4.1. A SwiftNIO application using TLS may be able to execute arbitrary code.

Affected Packages

1 total 1 fixed

Ecosystem	Package	Vulnerable range	Fix
📦SwiftURL	`github.com/apple/swift-nio-ssl`	≥ 2.0.0&&< 2.4.1	2.4.1

Detection & mitigation playbook

Open-source dependency

Detect
Scan your dependency tree (package-lock.json, pnpm-lock.yaml, requirements.txt, go.sum, etc.) for github.com/apple/swift-nio-ssl, including transitive dependencies — a direct dependency you never call can still pull in a vulnerable version.
Fix
Update github.com/apple/swift-nio-ssl to 2.4.1 or later, then make sure no transitive (indirect) dependency still pins the vulnerable range — O3 confirms CVE-2019-8849 is resolved across your whole dependency graph.
Workarounds
If you can't upgrade right away: gate or disable the affected feature, validate untrusted input at the boundary, and avoid passing attacker-controlled data into the vulnerable path. O3's runtime protection blocks exploitation in production as an interim safeguard until the upgrade lands.
How O3 protects you
O3 Security's impact-aware SCA analyses which vulnerable code paths your application actually calls, so a match like CVE-2019-8849 can be triaged on real exposure rather than presence alone.

Tailored to CVE-2019-8849. Runtime protection reduces exposure until a permanent patch is applied and verified — it complements patching, it doesn't replace it.

Frequently Asked Questions

The issue was addressed by signaling that an executable stack is not required. This issue is fixed in SwiftNIO SSL 2.4.1. A SwiftNIO application using TLS may be able to execute arbitrary code.

O3 Security · Impact-Aware SCA

Is CVE-2019-8849 in your dependencies?

O3 Security finds CVE-2019-8849 across SwiftURL dependencies, including transitive ones, and its impact-aware SCA ranks findings by whether your code actually calls the vulnerable path.

Scan my dependencies How O3 SCA works