VulnerabilityPublished 22 Oct 2026

CVE-2026-110354: HAProxy · Infinite Loop

Affects HAProxySource CVE Database V5

Not known to be exploited · CVSS 7.5 High · fixed in 3.5-dev9 : patch HAProxy soon.

Data as of 26 Oct 2026, 17:30 UTC

CVSS 3.1 base score

7.5High

How severe the flaw is on the 0–10 CVSS scale.

EPSS

0.8% chance of exploitation in 30 days – higher than 56% of CVEsExploit Prediction Scoring System: the likelihood attackers will use this flaw soon.

Exploitation: No evidence of active exploitation and no public proof of concept
Automatable: Attackers can reliably automate steps 1–4 of the kill chain
Technical impact: Limited control over the software or limited information exposure

CISA SSVC assessment, 2026-10-22.

Patch

Available – fixed in 3.5-dev9, 3.4.6, 3.3.17 +9

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

Attack Vector: Network
Attack Complexity: Low
Privileges Required: None
User Interaction: None
Scope: Unchanged
Confidentiality: None
Integrity: None
Availability: High

Bold values are the worst case: easiest to exploit or largest impact.

Attack Vector: Network: The vulnerable component is bound to the network stack and the set of possible attackers extends beyond the other options listed, up to and including the entire Internet. Such a vulnerability is often termed 'remotely exploitable' and can be thought of as an attack being exploitable at the protocol level one or more network hops away (e.g., across one or more routers).
Attack Complexity: Low: Specialized access conditions or extenuating circumstances do not exist. An attacker can expect repeatable success against the vulnerable component.
Privileges Required: None: The attacker is unauthorized prior to attack, and therefore does not require any access to settings or files to carry out an attack.
User Interaction: None: The vulnerable system can be exploited without any interaction from any user.
Scope: Unchanged: An exploited vulnerability can only affect resources managed by the same security authority. In this case, the vulnerable component and the impacted component are either the same, or both are managed by the same security authority.
Confidentiality: None: There is no loss of confidentiality within the impacted component.
Integrity: None: There is no loss of integrity within the impacted component.
Availability: High: There is total loss of availability, resulting in the attacker being able to fully deny access to resources in the impacted component; this loss is either sustained (while the attacker continues to deliver the attack) or persistent (the condition persists even after the attack has completed). Alternatively, the attacker has the ability to deny some availability, but the loss of availability presents a direct, serious consequence to the impacted component (e.g., the attacker cannot disrupt existing connections, but can prevent new connections; the attacker can repeatedly exploit a vulnerability that, in each instance of a successful attack, leaks a only small amount of memory, but after repeated exploitation causes a service to become completely unavailable).

Definitions: FIRST CVSS v3.1 specification.

Exploitation evidence

Disclosed: evidence found.
CVE published 22 Oct 2026
Detectable: no evidence on record.
No public nuclei template indexed
Weaponised: no evidence on record.
No public exploit code indexed in Metasploit or Exploit-DB
Exploited in the wildExploited: no evidence on record.
Not in CISA KEV and no source reports exploitation
Observed by OffSeq MirageSeen by Mirage: no evidence on record.
No attack traffic recorded by OffSeq Mirage sensors

A missing step is not evidence of safety. Sources: cve.org (opens in a new tab), the Metasploit, Exploit-DB and nuclei-templates index as of 26 Oct 2026.

Disclosed: The CVE record is public on cve.org. Its publication is t = 0.
Detectable: A public nuclei template can find exposed instances, for defenders and attackers alike.
Weaponised: Public exploit code exists in Metasploit or Exploit-DB, or CISA SSVC or the CVSS exploit maturity reports a public proof of concept.
Exploited in the wild: CISA KEV lists it, CISA SSVC rates exploitation active, or a source reports attacks.
Observed by OffSeq Mirage: OffSeq Mirage honeypot sensors recorded attack traffic for this CVE, or found exposed hosts without attack traffic.

Moments are spaced evenly, not to scale; a dashed line marks a gap of six months or more. Deltas count from t = 0. Sources that give only a date (CISA KEV, Exploit-DB, or a time of exactly 00:00Z) read “same day” rather than hours. Metasploit modules carry the flaw’s disclosure date, not their release date, and nuclei templates carry no date, so both appear above but not on the timeline.

What to do

Upgrade to a fixed release listed under Affected software.

Affected software

Product	Affected	Fixed in
HAProxyHAProxy	Affected >=3.5-dev <3.5-dev9	Fixed in 3.5-dev9
HAProxyHAProxy	Affected >=3.4.0 <3.4.6	Fixed in 3.4.6
HAProxyHAProxy	Affected >=3.3.0 <3.3.17	Fixed in 3.3.17
HAProxyHAProxy	Affected >=3.2.0 <3.2.26	Fixed in 3.2.26
HAProxyHAProxy	Affected >=3.0.0 <3.0.30	Fixed in 3.0.30
HAProxyHAProxy Enterprise Edition	Affected >=3.3r1 <3.3r1-377.1005	Fixed in 3.3r1-377.1005

AI-suggested

Upgrade HAProxy to one of the fixed versions: 3.4.6, 3.5-dev9, 3.3.17, 3.2.26, 3.0.30, or the corresponding patched releases in the 3.3r1, 3.2r1, and 3.0r1 branches. No other mitigations are indicated. Applying these official fixes fully resolves the issue.

Description

HAProxy versions prior to 3.4.6 contain an infinite loop vulnerability in the HTTP/1.1 chunked request parser. This flaw allows a remote unauthenticated attacker to cause a denial of service by exhausting CPU resources on worker threads. The affected threads remain at 100% CPU usage even after client disconnects and timeouts, potentially consuming all worker threads and requiring a process restart to recover.

Impact

The vulnerability results in denial of service through persistent CPU exhaustion on worker threads. This can degrade or completely disrupt HAProxy service availability, requiring a restart of the process to restore normal operation. There is no impact on confidentiality or integrity reported.

Summary

CVE-2026-110354 is a high-severity vulnerability in HAProxy versions before 3.4.6 where the HTTP/1.1 chunked request parser enters an infinite loop. Although the multiplexer drains the request before closing the stream, the parser repeatedly re-processes the same bytes without progress, causing persistent CPU exhaustion on worker threads. This denial of service can be triggered remotely without authentication and can consume all available worker threads, leading to service disruption until HAProxy is restarted. Fixed versions include 3.4.6 and later, as well as specific patched releases in the 3.0, 3.2, and 3.3 branches.

References

git.haproxy.org (opens in a new tab)

Community reviews

Loading reviews…

Exploitation evidence

What to do

Affected software

Description

AI analysisMachine-generated, updated 26 Oct 2026, 15:48 UTC

WeaknessesCWE-835

Technical details

References

Community reviews

Related threats