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Fencer Vulns
high 7.5

CVE-2026-90678 json

An issue was discovered in HAProxy 3.3.0 through 3.4.4 and in 3.5-dev1 through 3.5-dev5.

published 2026-09-13 57 d ago modified 2026-09-22 47 d ago also EUVD-2026-76943

cvss
7.5
version 3.1, CNA
cisa kev
Not listed
not in CISA's catalog
epss
0.8%
EPSS 0.8% chance of exploitation in 30 days, percentile 55%
public exploits
0
none known

Summary

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.

Patch / fix

  • HAProxy HAProxy 3.5-dev6
  • haproxy hummingbird 1 3.0.27-0.1.hum1

red hat advisories RHSA-2026:60634

Vendor advisories

What the vendors themselves say about their products: affected, fixed or not affected, and what to do.

red hat product security vex CVE-2026-90678 updated cvss 8.9

haproxy: HAProxy: HTTP Request Smuggling via HTTP/3 Multiplexer Desynchronization

  • Red Hat Hardened Images haproxy 3.0.27-0.1.hum1
    fixed: vendor fix RHSA-2026:60634
  • Red Hat Ceph Storage 5 haproxy, haproxy22 Red Hat Ceph Storage 9 rhceph-ci/haproxy, rhceph/rhceph-haproxy-rhel9 Red Hat Enterprise Linux 7 haproxy Red Hat Enterprise Linux 8 haproxy Red Hat Enterprise Linux 9 haproxy Red Hat Enterprise Linux 10 haproxy
    +2 more products
    Red Hat OpenShift Container Platform 4 haproxy, haproxy18, haproxy20, haproxy22, haproxy26, haproxy28 Red Hat OpenShift Container Platform 5 haproxy, haproxy32
    not affected: vulnerable code not present

Red Hat CSAF VEX © Red Hat, Inc., from https://security.access.redhat.com/data/csaf/v2/vex/; changed: reduced to product statuses and remediations. CC BY 4.0 · csaf

CISA SSVC

Exploitation
none
Automatable
no
Technical impact
partial
Assessed
56 d ago

Exploit prediction

0.77% chance of exploitation in the next 30 days, higher than 55% of all scored CVEs (FIRST EPSS, 2026-11-08).

CVSS scores

assigned by version score vector
CNA 3.1 7.5 CVSS:3.1/AV:N/AC:H/PR:N/UI:N/S:C/C:N/I:H/A:L

Affected products

  • HAProxy HAProxy

Classification

Weakness
  • CWE-130 Improper Handling of Length Parameter Inconsistency

References

Sources

Fencer Vulns keeps one entry per vulnerability: the CVE id wins, then GHSA, and records that alias each other are merged, except that two CVEs always keep separate entries. The same data is available as JSON.