Evidence used
- No CISA KEV confirmation is currently recorded.
- The selected CVSS metric records a network-reachable, unauthenticated path with no user interaction.
- EPSS is 0.77% for the current model date.
BlackTreeCVE IntelligenceFull vulnerability report · 2026
CVE-2026-90678High confidence
HAProxy: Improper Handling of Length Parameter Inconsistency
HAProxy · HAProxy
7.5HighCVSS 3.1
Within 7 days
Patch availableHigh technical severity; prioritise exposed affected systems while verifying vendor guidance.
R
Open reassessment dashboard →Operational reassessment
Published severity in operational context
Published severityHigh→Operational priority:High, unchanged from published severity.unchanged
Compensating controls
- Validate the affected product branch and deploy the verified fixed release.
- Restrict the affected network interface to trusted sources where business-safe.
- Monitor vendor guidance and exploitation sources for a material change.
Verification
- Confirm that the asset runs HAProxy HAProxy and falls inside the recorded affected range.
- Verify the installed build against the product-specific fixed version after deployment.
- Validate exposure, authentication requirements and compensating controls in the actual environment.
- Reopen this reassessment when CVSS, KEV, EPSS, exploit evidence or remediation changes.
Distribution package intelligence
4 package statesRelease-specific package status
Debian findings are scoped to the named distribution, release and source package. An absent finding does not mean a package is unaffected.
Repository candidate not checked
A published vendor fix does not prove that a matching update is enabled and installable on a particular asset. Confirm the local package candidate before scheduling remediation.
| Distribution release | Source package | Vendor state | Fixed version | Evidence |
|---|---|---|---|---|
| Debian trixietrixie · source | haproxy | Not affectedDebian marks this release not affected (fixed-version marker 0). | Not published in this feed | Debian Security Tracker ↗Source updated 5 Oct 2026 |
| Debian bookwormbookworm · source | haproxy | Not affectedDebian marks this release not affected (fixed-version marker 0). | Not published in this feed | Debian Security Tracker ↗Source updated 5 Oct 2026 |
| Debian forkyforky · source | haproxy | Not affectedDebian marks this release not affected (fixed-version marker 0). | Not published in this feed | Debian Security Tracker ↗Source updated 5 Oct 2026 |
| Debian sidsid · source | haproxy | Not affectedDebian marks this release not affected (fixed-version marker 0). | Not published in this feed | Debian Security Tracker ↗Source updated 5 Oct 2026 |
Direct vendor intelligence
1 currentAuthoritative vendor CSAF and VEX advisories
Structured product status and remediation from the issuing vendor. Product-state explanations are always visible; large lists can be searched or downloaded.
CVE-2026-90678 · CSAF 2.0 · revision 3 · finalRed Hat Product Securityhaproxy: HAProxy: HTTP Request Smuggling via HTTP/3 Multiplexer Desynchronization
The vendor explicitly identifies these products or versions as containing the fix.
- haproxy-0:3.0.27-0.1.hum1@aarch64 as a component of Red Hat Hardened Images
- haproxy-0:3.0.27-0.1.hum1@src as a component of Red Hat Hardened Images
- haproxy-0:3.0.27-0.1.hum1@x86_64 as a component of Red Hat Hardened Images
- Summary
- A flaw was found in HAProxy. A remote, unauthenticated attacker can exploit a vulnerability in the HTTP/3 multiplexer when processing requests without a Content-Length header, leading to HTTP request smuggling. This occurs when HAProxy is configured with QUIC support and an HTTP/3 frontend, and traffic is routed to a backend over HTTP/1.1 using chunked transfer coding on a reused connection. Successful exploitation allows the attacker to bypass frontend security rules and potentially intercept or cause the loss of other clients' requests, including sensitive information like authentication credentials.
- Remediation
- For details on how to apply this update, which includes the changes described in this advisory, refer to: https://images.redhat.com/
High technical severity; prioritise exposed affected systems while verifying vendor guidance.
Patch available01
What, why and how
An issue was discovered in HAProxy 3.3.0 through 3.4.4 and in 3.5-dev1 through 3.5-dev5. Exploitation requires an HTTP/3 frontend: HAProxy must be built with QUIC support and configured with a QUIC bind listener, and the affected traffic must reach a backend over HTTP/1.1 using chunked transfer coding on a reused connection. Under those conditions, when an HTTP/3 request carries no Content-Length header, the HTTP/3 multiplexer credits the length declared in a DATA frame header to the stream endpoint's known-input-payload estimate at the moment the frame header is decoded, before the payload has been received, and that declared length is emitted verbatim as the HTTP/1.1 chunk size. A remote unauthenticated client that declares more payload than it delivers and then ends the stream causes HAProxy to announce a chunk larger than the bytes it writes and to return the connection to the idle pool in a desynchronized state. The result is potential HTTP request smuggling on reused backend connections: an attacker can place a request past a frontend rule such as a path-based http-request deny, so that the smuggled request is never seen by HAProxy's HTTP analysis, and can cause concurrent clients' requests, including their request lines and Authorization headers, to be consumed as the attacker's request body and lost. Exploitation is not deterministic; it depends on a race with backend connection pooling, succeeding in a majority of but not all trials during testing, and can be retried freely. The mechanism was introduced in 3.3-dev10; releases 3.2.x and earlier are unaffected.
What
An issue was discovered in HAProxy 3.3.0 through 3.4.4 and in 3.5-dev1 through 3.5-dev5. Exploitation requires an HTTP/3 frontend: HAProxy must be built with QUIC support and configured with a QUIC bind listener, and the affected traffic must reach a backend over HTTP/1.1 using chunked transfer coding on a reused connection. Under those conditions, when an HTTP/3 request carries no Content-Length header, the HTTP/3 multiplexer credits the length declared in a DATA frame header to the stream endpoint's known-input-payload estimate at the moment the frame header is decoded, before the payload has been received, and that declared length is emitted verbatim as the HTTP/1.1 chunk size. A remote unauthenticated client that declares more payload than it delivers and then ends the stream causes HAProxy to announce a chunk larger than the bytes it writes and to return the connection to the idle pool in a desynchronized state. The result is potential HTTP request smuggling on reused backend connections: an attacker can place a request past a frontend rule such as a path-based http-request deny, so that the smuggled request is never seen by HAProxy's HTTP analysis, and can cause concurrent clients' requests, including their request lines and Authorization headers, to be consumed as the attacker's request body and lost. Exploitation is not deterministic; it depends on a race with backend connection pooling, succeeding in a majority of but not all trials during testing, and can be retried freely. The mechanism was introduced in 3.3-dev10; releases 3.2.x and earlier are unaffected.
Why
The product parses a formatted message or structure, but it does not handle or incorrectly handles a length field that is inconsistent with the actual length of the associated data.
How
An attacker operating through a network path may attempt exploitation without authentication or user interaction. If successful, the issue may cause the confidentiality, integrity or availability impact described by the vendor.
What
An issue was discovered in HAProxy 3.3.0 through 3.4.4 and in 3.5-dev1 through 3.5-dev5. Exploitation requires an HTTP/3 frontend: HAProxy must be built with QUIC support and configured with a QUIC bind listener, and the affected traffic must reach a backend over HTTP/1.1 using chunked transfer coding on a reused connection. Under those conditions, when an HTTP/3 request carries no Content-Length header, the HTTP/3 multiplexer credits the length declared in a DATA frame header to the stream endpoint's known-input-payload estimate at the moment the frame header is decoded, before the payload has been received, and that declared length is emitted verbatim as the HTTP/1.1 chunk size. A remote unauthenticated client that declares more payload than it delivers and then ends the stream causes HAProxy to announce a chunk larger than the bytes it writes and to return the connection to the idle pool in a desynchronized state. The result is potential HTTP request smuggling on reused backend connections: an attacker can place a request past a frontend rule such as a path-based http-request deny, so that the smuggled request is never seen by HAProxy's HTTP analysis, and can cause concurrent clients' requests, including their request lines and Authorization headers, to be consumed as the attacker's request body and lost. Exploitation is not deterministic; it depends on a race with backend connection pooling, succeeding in a majority of but not all trials during testing, and can be retried freely. The mechanism was introduced in 3.3-dev10; releases 3.2.x and earlier are unaffected.
Why
The product parses a formatted message or structure, but it does not handle or incorrectly handles a length field that is inconsistent with the actual length of the associated data.
How
An attacker operating through a network path may attempt exploitation without authentication or user interaction. If successful, the issue may cause the confidentiality, integrity or availability impact described by the vendor.
02
Exploit reality and attack path
CVSS severity, EPSS forecast probability, public exploit material and CISA-confirmed exploitation are separate signals.
Observed exploitation No confirmed evidence
?
Confirmed exploitation and public exploit material are separate signals. Attacks can occur without public proof-of-concept or exploit code.No CISA KEV match was present at the last successful refresh. This means no confirmation from that source, not proof of no exploitation.
Public PoC / exploit material None recorded
?
Confirmed exploitation and public exploit material are separate signals. Attacks can occur without public proof-of-concept or exploit code.No exploit-tagged reference or CISA SSVC proof-of-concept state is currently recorded. Research may still exist outside the structured feeds.
- Likely attack path
- a network path → Improper Handling of Length Parameter Inconsistency → cause the confidentiality, integrity or availability impact described by the vendor
- Attack surface
- Network
- Privileges required
- None: unauthenticated exploitation is possible
- User interaction
- None
- Attack complexity
- High: exploitation depends on specific conditions
- Security boundary
- Changed: exploitation can affect a different security authority
- Weakness
?
CWE means Common Weakness Enumeration: a standard category for the underlying weakness. - CWE-130 ↗
CWE-130: Improper Handling of Length Parameter Inconsistency. The product parses a formatted message or structure, but it does not handle or incorrectly handles a length field that is inconsistent with the actual length of the associated data.
- CVSS vector
?
CVSS means Common Vulnerability Scoring System. The vector records the metric values used to calculate technical severity. CVSS:3.1/AV:N/AC:H/PR:N/UI:N/S:C/C:N/I:H/A:LCommon Vulnerability Scoring System 3.1: the compact vector below is decoded into plain language.
AVNetworkAttack vector: The vulnerable component can be reached over a network.ACHighAttack complexity: Successful exploitation depends on specific conditions outside the attacker's direct control.PRNonePrivileges required: The attacker does not need an account or existing privileges.UINoneUser interaction: No action by another user is required.SChangedScope: The attack can affect a component governed by a different security authority.CNoneConfidentiality impact: No direct loss is represented by this metric.IHighIntegrity impact: A successful attack can cause a major loss.ALowAvailability impact: A successful attack can cause a limited loss.- Post-exploitation / living off the land
- No specific living-off-the-land technique is confirmed in the structured sources. Monitor normal administration tools for activity inconsistent with the affected service's baseline.
03
Patch and workaround
Operational remediation based on structured source evidence.
- Status
?
Patch availability is based on structured fixed-version fields and authoritative update references. If no fix is verified, check the vendor advisory before making a change. - Patch available
- Fixed
- Action
- For details on how to apply this update, which includes the changes described in this advisory, refer to: https://images.redhat.com/
- Workaround
- No verified workaround is recorded. If business-safe, reduce exposure to the affected interface and allow only trusted sources until authoritative guidance is available.
04
Evidence and provenance
Published 13 Sept 2026 · Last source change 14 Sept 2026, 15:48 UTC · CWE-130 · Improper Handling of Length Parameter Inconsistency
CVE recordCVE.org · 5.2
CVSS sourceCNA
EPSS source FIRST · tracked since 2026-09-14
?
The date BlackTree first stored a score for this CVE from the daily FIRST EPSS feed.European sourceENISA EUVD · EUVD-2026-76943
Product sourceCNA
Remediation sourceVendor CSAF · Red Hat Product Security
CWE sourceCNA
NVD statusNVD awaiting enrichment
Core structured fields are present and their contributing authorities are shown above.
Material change intelligence
View recent updates ↗What changed after publication
- Vendor guidanceAuthoritative vendor guidance changed from remediation: access.redhat.com/CVE-2026-90678 to remediation: access.redhat.com/CVE-2026-90678.Red Hat Product Security ↗
- Before
- remediation: access.redhat.com/CVE-2026-90678
- After
- remediation: access.redhat.com/CVE-2026-90678
- Remediation statusRemediation status changed from Mitigation available to Patch available.Red Hat Product Security ↗
- Before
- Mitigation available
- After
- Patch available
- Affected versionsThe structured affected or fixed version information changed.Red Hat Product Security ↗
- Before
- haproxy.src as a component of Red Hat Hardened Images
- After
- Fixed: haproxy-0:3.0.27-0.1.hum1@aarch64 as a component of Red Hat Hardened Images; haproxy-0:3.0.27-0.1.hum1@src as a component of Red Hat Hardened Images; haproxy-0:3.0.27-0.1.hum1@x86_64 as a component of Red Hat Hardened Images
- Vendor guidanceAuthoritative vendor guidance changed from remediation: access.redhat.com/CVE-2026-90678 to remediation: access.redhat.com/CVE-2026-90678.Red Hat Product Security ↗
- Before
- remediation: access.redhat.com/CVE-2026-90678
- After
- remediation: access.redhat.com/CVE-2026-90678
- Remediation statusRemediation status changed from Awaiting fix to Mitigation available.Red Hat Product Security ↗
- Before
- Awaiting fix
- After
- Mitigation available
- ENISA EUVD mappingEUVD-2026-76943 was added to the official ENISA EUVD mapping for this CVE.ENISA EUVD ↗
- Before
- not recorded
- After
- {"euvdId":"EUVD-2026-76943"}
- Catalogue recordCVE added to the BlackTree catalogue.CNA ↗
CVE published
Fixed release or patch reference recorded
Technical terms and abbreviations used in this report
- CVE
- Common Vulnerabilities and Exposures: the public identifier for one disclosed vulnerability.
- CVSS
- Common Vulnerability Scoring System: a technical severity framework; it is not patching priority by itself.
- EPSS
- Exploit Prediction Scoring System: FIRST's estimate of the probability that exploitation activity will be observed in the next 30 days; it is a forecast, not confirmation.
- CWE
- Common Weakness Enumeration: the standard category describing the underlying software or hardware weakness.
- CNA
- CVE Numbering Authority: an organisation authorised to assign and publish CVE records.
- CISA ADP
- Cybersecurity and Infrastructure Security Agency Authorized Data Publisher: structured enrichment added to a CVE record.
- NVD
- National Vulnerability Database: NIST's enrichment service for CVE records.
- CERT / CSIRT
- A computer security incident response team that publishes warnings or coordinates incident response.
- PoC
- Proof of concept: public material that demonstrates or helps reproduce exploitation.
- CSAF
- Common Security Advisory Framework: a machine-readable format for security advisories.
- LoTL
- Living off the land: abuse of legitimate tools or system functions during an attack.