`CVE-2026-54556`

8.2 High No exploit published

Published 20 days ago. NVD backfills CPE data for days or weeks after publication, and OSV and the exploit indexes lag too. Scope and status here may change.

Description

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.

CWE-409

Exploitation Status

No public exploit

Nothing published shows this CVE being exploited, which is not the same as ruling it out.

CVSS E:U

CISA KEV not listed
CISA Vulnrichment exploitation: none
Indexed PoC none indexed
EPSS 0.30% chance in 30 days

Waratek Defense Posture

No exploit published

In RASP's scope with an upstream fix path, but nobody has published a working exploit. That is a statement about what has been published, not a finding that the defect is unreachable or unimportant.

Protection none
Action unverified patch rule
Review automated upstream-data
Record active

Decided by no-exploit-published : A published working exploit for this candidate, not only a proof of concept, a forecast, or nothing at all

Finding This CVE is not listed in CISA KEV, CISA Vulnrichment records no active exploitation, and no reviewed exploit catalogue carries an entry for it. Nobody has published something a stranger can run, so it is not a candidate for a rule ahead of the ones where somebody has; an upstream fix path does exist, so the remediation half of the candidacy still holds. This is a statement about what has been published, not about whether the defect is reachable or serious.

Candidate fix https://github.com/http4s/http4s/commit/6e8eccd64a6a74ab4811897881e95e0e1b3a818e : a commit: the change itself

Decided by	`no-exploit-published` : A published working exploit for this candidate, not only a proof of concept, a forecast, or nothing at all
Finding	This CVE is not listed in CISA KEV, CISA Vulnrichment records no active exploitation, and no reviewed exploit catalogue carries an entry for it. Nobody has published something a stranger can run, so it is not a candidate for a rule ahead of the ones where somebody has; an upstream fix path does exist, so the remediation half of the candidacy still holds. This is a statement about what has been published, not about whether the defect is reachable or serious.
Candidate fix	https://github.com/http4s/http4s/commit/6e8eccd64a6a74ab4811897881e95e0e1b3a818e : a commit: the change itself

CVSS

8.2 HIGH v4.0

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/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:X

1 metric

VRT selects the newest version's highest entry and publishes it as cvssScore, newest rather than largest because scores are not comparable across versions, and highest rather than first because the first entry is frequently a CNA placeholder scoring 0.0 over NVD's own analysis.

Version Score Band Vector Assigner Type

CVSS 4.0 8.2 HIGH 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/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:X security-advisories@github.com Secondary published

Version	Score	Band	Vector	Assigner	Type
CVSS 4.0	8.2	HIGH	`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/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:X`	security-advisories@github.com	Secondary	published

Affected Software & Releases

☕ Maven Library Packages

Artifact coordinates and fix boundaries from OSV.dev

Package Coordinate Introduced Fixed Last affected

org.http4s:http4s-ember-core_2.12 0 0.23.35 unbounded

org.http4s:http4s-ember-core_2.13 1.0.0-M1 1.0.0-M47 unbounded

org.http4s:http4s-ember-core_3 0 0.23.35 unbounded

org.http4s:http4s-ember-core_3 1.0.0-M1 1.0.0-M47 unbounded

org.http4s:http4s-ember-core_2.13 0 0.23.35 unbounded

Package Coordinate	Introduced	Fixed	Last affected
`org.http4s:http4s-ember-core_2.12`	0	`0.23.35`	unbounded
`org.http4s:http4s-ember-core_2.13`	1.0.0-M1	`1.0.0-M47`	unbounded
`org.http4s:http4s-ember-core_3`	0	`0.23.35`	unbounded
`org.http4s:http4s-ember-core_3`	1.0.0-M1	`1.0.0-M47`	unbounded
`org.http4s:http4s-ember-core_2.13`	0	`0.23.35`	unbounded

🖥️ Product CPEs & Version Ranges

3 product(s) over 5 version claims (uncapped)

Source	Vendor	Product	Scheme	Affected Versions
osv	org.http4s	http4s-ember-core_2.12	generic	＜ 0.23.35
osv	org.http4s	http4s-ember-core_2.13	generic	＜ 0.23.35 · ≥ 1.0.0 and ＜ 1.0.0
osv	org.http4s	http4s-ember-core_3	generic	＜ 0.23.35 · ≥ 1.0.0 and ＜ 1.0.0

Source

Vendor

Product

Scheme

Affected Versions

osv

org.http4s

http4s-ember-core_2.12

generic

＜ 0.23.35

osv

org.http4s

http4s-ember-core_2.13

generic

＜ 0.23.35 · ≥ 1.0.0 and ＜ 1.0.0

osv

org.http4s

http4s-ember-core_3

generic

＜ 0.23.35 · ≥ 1.0.0 and ＜ 1.0.0

References

URL	Tags
https://github.com/http4s/http4s/commit/6e8eccd64a6a74ab4811897881e95e0e1b3a818e	commit
https://github.com/http4s/http4s/security/advisories/GHSA-vmm3-xgcx-67hm	WEB
https://github.com/http4s/http4s	PACKAGE
https://github.com/http4s/http4s/releases/tag/v0.23.35	WEB
https://github.com/http4s/http4s/releases/tag/v1.0.0-M47	WEB

URL

Timeline

Published 2026-08-26 Last modified 2026-09-09

Published	2026-08-26	By the CVE Program.
NVD record modified	2026-09-09	NVD's own last-modified date for this record.

Published

2026-08-26

By the CVE Program.

NVD record modified

2026-09-09

NVD's own last-modified date for this record.

Pipeline policy audit (15 of 21 rules evaluated)

15 of 21 rules ran. The rest were never reached, because an earlier stage settled the CVE, a distinct claim from a rule that ran and found nothing.

# Rule Outcome Status Detail

identity: Does this identifier describe a vulnerability at all? first match wins

1 rejected no-match CVE Program withdrawal of this identifier

scope: Is the vulnerability ARMR's to address? first match wins

2 armr-patch-file no-match An ARMR patch file on disk for this CVE

3 armr-secure-rule-file no-match An ARMR security-rule template on disk for this CVE

4 manual-classification no-match A researcher's recorded decision for this specific CVE

5 manual classification no-match Manual classification of this CVE in the legacy dataset

6 non-java-upstream no-match A root cause in non-Java code: an OS kernel, a C library, or a bundled runtime

7 oracle-component no-match The defect being in a component of a tracked product the agent does not reach: JavaFX, the Java SE installer, the native WebLogic proxy plug-in. Oracle gives these no CPE of their own and names them only in the description.

8 osv-maven matched Queued for review Maven packages: org.http4s:http4s-ember-core_2.12, org.http4s:http4s-ember-core_2.13, org.http4s:http4s-ember-core_3

9 cna-maven-package not-reached An affected Maven artifact named by the CNA itself

10 known-cpe-product not-reached An NVD CPE naming a product ARMR tracks

11 cna-cpe-product not-reached A CPE the CNA published naming a tracked product. Oracle publishes these on advisory day, months before NVD.

12 oracle-advisory-family not-reached A tracked product family named in Oracle's own risk matrix. CPE cannot carry a suite name, only a module.

13 non-deployable-product not-reached The only affected product being a sealed appliance image, where Java runs but no -javaagent can be attached

14 unmatched-product not-reached No tracked product matched above, and none present at all

disposition: What do we do about one that is? cumulative: every rule gets a turn

15 patch-hint matched Mitigation candidate References include candidate fix URL (commit tier): https://github.com/http4s/http4s/commit/6e8eccd64a6a74ab4811897881e95e0e1b3a818e

16 open-source-maven skipped The affected package being open source on Maven, so the fix can be read

17 poc-derivable skipped An indexed exploit to reverse-engineer, where there is no source to read

18 no-exploit skipped With no fix path, a public exploit, or a CISA record of one

19 secure-rule-match no-match A vulnerability class already blocked by an ARMR security rule

20 below-action-threshold no-match Severity is HIGH — only MEDIUM/LOW are deprioritized

21 no-exploit-published decided it matched No exploit published No working exploit has been published, and an upstream fix path does exist, so the remediation half of the candidacy still holds.

Raw stored JSON document for this CVE ↗ · NVD ↗ · CVE.org ↗