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CVE-2026-54556Suited to automated attack · CISA

Http4s: HTTP/2 Denial of Service with Ember Backend

CVSS score

8.2

EPSS probability

%0.5

Risk score

0.0

Published

1 mo ago

OverviewPublic Exploits (0)NewsroomVulnerability Timeline
Official patch verified

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Vulnerability description

DayBreach CVE AI Research

CVE-2026-54556 has vendor, distribution, patch and security-source records on file. We can compare them and prepare an explanation linked to the evidence.

Http4s is a Scala interface for HTTP services. Prior to 0.23.35 and 1.0.0-M47, an unauthenticated HTTP/2 peer can cause an out-of-memory denial of service in the Ember backend with HTTP/2 enabled. The Hpack wrapper in ember-core/shared/src/main/scala/org/http4s/ember/core/h2/Hpack.scala concatenates HEADERS and CONTINUATION frame fragments and decodes them into a single List, but maxHeaderSize accounting does not include indexed headers or HPACK per-header overhead. A small compressed header block can therefore expand into a much larger decoded representation that remains in memory for processing. Servers exposed to untrusted HTTP/2 traffic and clients directed to an untrusted HTTP/2 server are affected, and concurrent malicious connections can exhaust the process heap. This issue is fixed in versions 0.23.35 and 1.0.0-M47.

IMPACT: Affected Products and Software

Affected Products

The following products are affected by CVE-2026-54556 vulnerability. Where our threat engine knows the exact affected versions, they are listed below.

IDVENDORPRODUCTACTION
1http4shttp4s View
2org.http4shttp4s-ember-core_2.12 View
3org.http4shttp4s-ember-core_2.13 View
4org.http4shttp4s-ember-core_3 View
5mavenorg.http4s:http4s-ember-core_2.12 View
6mavenorg.http4s:http4s-ember-core_2.13 View
7mavenorg.http4s:http4s-ember-core_3 View
8mavenorg.http4s:http4s-ember-core_3 View
9mavenorg.http4s:http4s-ember-core_2.13 View
10mavenorg.http4s:http4s-ember-core_2.12 View
11mavenorg.http4s:http4s-ember-core_2.13 View
12mavenorg.http4s:http4s-ember-core_3 View
13mavenorg.http4s:http4s-ember-core_3 View
14mavenorg.http4s:http4s-ember-core_2.13 View
Total affected vendors: 3|Products: 14

RED HAT CSAF/VEX: Product Impact Check

Red Hat has not yet published a CSAF/VEX impact record for this CVE. This does not mean “not affected”.

SCORING: CVSS from Multiple Sources

CVSS Scores

The Common Vulnerability Scoring System is a standardised framework for assessing the severity of vulnerabilities in software and systems. We collect and display CVSS scores from several sources for each CVE.

SCOREVERSIONSEVERITYVECTORSOURCE
8.2CVSS 4.0—Vector not publishedGitHub Advisory
8.2CVSS V4_0HIGHCVSS:4.0/AV:N/AC:L/AT:P/PR:N/UI:N/VC:N/VI:N/VA:H/SC:N/SI:N/SA:NCVE CNA
8.2CVSS V40HIGHCVSS:4.0/AV:N/AC:L/AT:P/PR:N/UI:N/VC:N/VI:N/VA:H/SC:N/SI:N/SA:N/E:X/CR:X/IR:X/AR:X/MAV:X/MAC:X/MAT:X/MPR:X/MUI:X/MVC:X/MVI:X/MVA:X/MSC:X/MSI:X/MSA:X/S:X/AU:X/R:X/V:X/RE:X/U:XNVD

Patch and Remediation Guide

Solution & Remediation Advisory

Patch verified

5 doğrulanmış yama veya düzeltilmiş sürüm kanıtı bulundu.

osvorg.http4s:http4s-ember-core_2.120.23.35

OSV düzeltilmiş sürüm: 0.23.35

osvorg.http4s:http4s-ember-core_2.131.0.0-M47

OSV düzeltilmiş sürüm: 1.0.0-M47

osvorg.http4s:http4s-ember-core_30.23.35

OSV düzeltilmiş sürüm: 0.23.35

osvorg.http4s:http4s-ember-core_31.0.0-M47

OSV düzeltilmiş sürüm: 1.0.0-M47

osvorg.http4s:http4s-ember-core_2.130.23.35

OSV düzeltilmiş sürüm: 0.23.35

Confirm the affected product and version against the source evidence above.
Restrict access to internet-facing services and apply network segmentation.
Apply the official update named in the evidence only to the matching product and version.
Monitor server logs and network endpoints for signs of anomalous execution.

Public exploit and active exploitation status

Verified exploit intelligence

No verified public PoC, exploit repository or Metasploit module has been found for this CVE yet.

Weakness Classification and Attack Patterns (CWE & CAPEC)

CWE - Common Weakness Enumeration

While CVE identifies specific instances of vulnerabilities, CWE categorises the common flaws or weaknesses that can lead to vulnerabilities. CVE-2026-54556 is associated with the following CWEs:

CWE-409: Common Weakness Enumeration Entry CWE-409

Common Attack Pattern Enumeration and Classification (CAPEC)

Common Attack Pattern Enumeration and Classification (CAPEC) stores attack patterns, which are descriptions of the common attributes and approaches employed by adversaries to exploit the CVE-2026-54556 weaknesses.

CAPEC-66: SQL InjectionCAPEC-126: Path TraversalCAPEC-28: OS Command Injection

Attack Vector and Accessibility

ExposureAğ üzerinden
PermissionsGerekmiyor
UserGerekmiyor

Official Sources and Advisories

https://github.com/http4s/http4s/security/advisories/GHSA-vmm3-xgcx-67hmvendor-advisoryhttps://github.com/http4s/http4s/commit/6e8eccd64a6a74ab4811897881e95e0e1b3a818evendor-advisoryhttps://github.com/http4s/http4s/releases/tag/v0.23.35vendor-advisoryhttps://github.com/http4s/http4s/releases/tag/v1.0.0-M47vendor-advisoryhttps://github.com/advisories/GHSA-vmm3-xgcx-67hmvendor-advisoryhttps://github.com/http4s/http4svendor-advisory

CVSS Vector Radar Chart

8.2 / 10
Attack VectorNetworkComplexityLowPrivilegesNoneUser Interact.NoneConfidentialityLowIntegrityNoneAvailabilityHigh

Vulnerability Scoring Details

CVSS:4.0/AV:N/AC:L/AT:P/PR:N/UI:N/VC:N/VI:N/VA:H/SC:N/SI:N/SA:N
Attack VectorNetwork
Attack ComplexityLow
Privileges RequiredNone required
User InteractionNone required
Confidentiality (Gizlilik)Low
Integrity (Bütünlük)None
Availability (Erişilebilirlik)High

Yama doğrulandı

5 doğrulanmış yama veya düzeltilmiş sürüm kanıtı bulundu.

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Weakness Type (CWE & CAPEC)

CWE-409

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