CVE-2026-90678 (CVSS 7.5)

Description

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.

Is your site exposed to CVE-2026-90678?

Run a free security scan — no signup, results in seconds.

CVSS v3.1 Score

7.5

HIGH

CVSS:3.1/AV:N/AC:H/PR:N/UI:N/S:C/C:N/I:H/A:L

EPSS — Exploit Prediction

0.0077

Probability of exploitation

0.54%

Percentile rank

EPSS estimates the probability that this vulnerability will be exploited in the wild within the next 30 days. A higher score means more likely to be exploited.

Weakness Type (CWE)

CWE-130 CWE-130

References

Other References

http://git.haproxy.org/?p=haproxy.git;a=commit;h=86a4ebc761a278838e8cb06f3a292282ba704c65 https://github.com/haproxy/haproxy/commit/86a4ebc761a278838e8cb06f3a292282ba704c65 https://www.haproxy.org/download/3.5/src/CHANGELOG

Frequently Asked Questions

What is CVE-2026-90678? +

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. It has a CVSS v3.1 base score of 7.5 (HIGH).

How severe is CVE-2026-90678? +

CVE-2026-90678 has a CVSS v3.1 score of 7.5 out of 10, rated HIGH. This is a high-severity vulnerability that should be prioritized for patching. The EPSS score is 0.0077, placing it in the 1th percentile for exploitation probability.

How do I check if I'm vulnerable to CVE-2026-90678? +

You can use Secably's free Website Scanner to check your website for known vulnerabilities. For infrastructure scanning, use the Port Scanner to identify exposed services that may be affected. Check the vendor advisories linked above for specific patch and version information.

Related Vulnerabilities

CVE-2026-94633

Memory allocation with excessive size value, Improper handling of length parameter inconsistency vulnerability in Apache Thrift Dart bindings. This issue …

CVE-2026-5706

In Bluetooth Mesh SDK 6.1.4 and earlier, malformed extended advertisements can trigger out-of-bounds writes leading to stack corruption and remote …

CVE-2026-9054

An attacker sending tcp, il, rudp, rudp, or gre packets with a length less than the header size would trigger …

CVE-2026-14587

Neo4j's Bolt modern handshake decoder treats an overlong capability bit mask the same way it treats a truncated bit mask. …

CVE-2026-48487

Zeroconf is a pure Python implementation of multicast DNS service discovery. Prior to 0.149.16, _read_character_string and _read_string in src/zeroconf/_protocol/incoming.py advanced …

CVE-2026-110912

In DragonFly BSD through 6.4.2 before 4bb22ff, the ARP input handlers arpintr() and in_arpinput() (sys/netinet/if_ether.c) do not validate the hardware …