CVE-2026-54428
HIGHCVE-2026-54428 is a high-severity (CVSS 7.5) Uncontrolled Resource Consumption vulnerability in org.apache.httpcomponents.core5:httpcore5-h2. O3 Security confirms whether CVE-2026-54428 is actually reachable in your code before you act, and blocks exploitation at runtime until you patch.
Apache HttpComponents Core: HPackDecoder Unlimited Header List Size Before SETTINGS ACK
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 CVE-2026-54428.
EPSS Exploitation Probability
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-2026-54428 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 360,482 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
org.apache.httpcomponents.core5:httpcore5-h2☕org.apache.httpcomponents.core5:httpcore5-h2Real-time download stats are indexed for npm and PyPI packages. This vulnerability affects Maven packages — download data is not available via public APIs for these ecosystems.
Description
Allocation of resources without limits or throttling in the HTTP/2 HPACK decoder in Apache HttpComponents Core (5.4.2 and earlier, 5.5-beta1 and earlier) allows an remote attacker to cause a denial of service through memory exhaustion by sending oversized compressed header blocks before the HTTP/2 SETTINGS acknowledgement causes the configured header list size limit to be applied.
Affected Packages
| Ecosystem | Package | Vulnerable range | Fix |
|---|---|---|---|
| ☕Maven | org.apache.httpcomponents.core5:httpcore5-h2 | all versions | 5.4.3 |
| ☕Maven | org.apache.httpcomponents.core5:httpcore5-h2 | ≥ 5.5-alpha1&&< 5.5-beta2 | 5.5-beta2 |
Detection & mitigation playbook
Open-source dependencyDetect
Scan your dependency tree (package-lock.json, pnpm-lock.yaml, requirements.txt, go.sum, etc.) for org.apache.httpcomponents.core5:httpcore5-h2. O3's reachability analysis confirms whether the vulnerable code path is actually invoked in your application, so you act on real exposure instead of every transitive match.
Fix
Update org.apache.httpcomponents.core5:httpcore5-h2 to 5.4.3 or later, then make sure no transitive (indirect) dependency still pins the vulnerable range — O3 confirms CVE-2026-54428 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 pinpoints whether CVE-2026-54428 is reachable in your code and exactly where to fix it, then blocks exploitation in production at runtime until the patched version is deployed.
Tailored to CVE-2026-54428. Runtime protection reduces exposure until a permanent patch is applied and verified — it complements patching, it doesn't replace it.
Fixing This On Your OS
If you run this on a Linux distribution, patch through your package manager against the distro's own security advisory below — it tracks the exact backported fix for your release, which can ship on a different timeline (and sometimes a different severity) than the upstream project.
This is an Important denial of service vulnerability in Apache HttpComponents Core. The HTTP/2 HPACK decoder is susceptible to memory exhaustion when processing oversized compressed header blocks from a remote attacker. This occurs before the system's configured header list size limits are applied, potentially…
Frequently Asked Questions
Is CVE-2026-54428 in your dependencies?
O3 detects CVE-2026-54428 across Maven dependencies and uses function-level reachability to confirm whether the vulnerable code path is actually reachable — not just present. No false positives.