HAProxy: Unchecked Return Value
CVE-2026-110353 is a high-severity unchecked return value vulnerability in HAProxy, with a CVSS 3.1 base score of 7.5 out of 10. It can be exploited remotely over the network by an unauthenticated attacker, without any action from a user. The record lists versions 3.2.26, 3.3.17, 3.4.6 as the first without the flaw, so updating HAProxy to one of those releases or later removes the exposure. There is no confirmed exploitation so far. EPSS estimates a 0.74% chance of exploitation within 30 days, higher than 55% of scored CVEs.
High severity with no evidence of exploitation so far.
What to do
- Update HAProxy to 3.2.26 or 3.3.17 or 3.4.6 or 3.5-dev9, whichever matches your release line, or a later version.
- Update HAProxy Enterprise Edition to 3.2r1-378.1259 or 3.3r1-377.1005, whichever matches your release line, or a later version.
- Update Kubernetes Ingress Controller to 3.2.17 or a later version.
- Until you can update, restrict network access to the affected service so it is not reachable from untrusted networks.
Affected products and versions
| Vendor | Product | Affected versions | Fixed in |
|---|---|---|---|
| HAProxy | HAProxy | 3.2.0 up to, but not including, 3.2.26; 3.3.0 up to, but not including, 3.3.17; 3.4.0 up to, but not including, 3.4.6; 3.5-dev up to, but not including, 3.5-dev9 | 3.2.26, 3.3.17, 3.4.6, 3.5-dev9 |
| HAProxy | HAProxy Enterprise Edition | 3.2.0r1 up to, but not including, 3.2r1-378.1259; 3.3.0r1 up to, but not including, 3.3r1-377.1005 | 3.2r1-378.1259, 3.3r1-377.1005 |
| HAProxy | Kubernetes Ingress Controller | 3.2.0 up to, but not including, 3.2.17 | 3.2.17 |
| Haproxy | Kubernetes Ingress Controller Enterprise | 3.2.0 up to, but not including, 3.2.17-ee1; 3.0 up to, but not including, 3.0.16-ee17; 1.11 up to, but not including, 1.11.14-ee11 | 3.2.17-ee1, 3.0.16-ee17, 1.11.14-ee11 |
Version data comes from the organisation that assigned the CVE. Confirm against the vendor advisory before deciding you are unaffected.
How the severity score breaks down
- Attack vector
- NetworkCan be exploited remotely over a network, including the internet.
- Attack complexity
- LowNo special conditions are needed; the attack works reliably.
- Privileges required
- NoneNo account or login is needed.
- User interaction
- NoneNo action by a victim is required.
- Scope
- UnchangedImpact stays within the vulnerable component.
- Confidentiality
- NoneNo data is disclosed.
- Integrity
- NoneNothing can be modified.
- Availability
- HighThe component can be taken down completely.
Vector: CVSS:3.1/AV:N/AC:L/PR:N/UI:N/S:U/C:N/I:N/A:H. Scored by CNA (mitre.org).
Official description
HAProxy 3.2 before 3.4.6 allows a remote unauthenticated attacker to cause a denial of service (worker-thread CPU exhaustion) via a truncated HTTP/2 PING frame. h2c_handle_ping in src/mux_h2.c does not check for a short read, unlike the other H2 frame handlers. Because the incomplete frame cannot be processed, its data is never consumed, and the H2 multiplexer tasklet is repeatedly woken by that pending data without making progress. The CPU spins until timeout http-request closes the connection, and an attacker opening many such connections can sustain high CPU usage.
Source: the CVE record as published by its numbering authority, via NVD and CVE.org.
The underlying weakness: Unchecked Return Value
The product does not check the return value from a method or function.
How developers prevent this class of flaw
- Check the results of all functions that return a value and verify that the value is expected.
- For any pointers that could have been modified or provided from a function that can return NULL, check the pointer for NULL before use. When working with a multithreaded or otherwise asynchronous environment, ensure that proper locking APIs are used to lock before the check, and unlock when it has finished.
- Ensure that you account for all possible return values from the function.
Timeline
- CVE record published.
- CISA published its SSVC assessment (exploitation: none, automatable: yes, technical impact: partial).
References
Other vulnerabilities in HAProxy
- 7.5 High severity
- 7.5 High severity
- 7.5 High severity
- 9.1 Critical severity
- 7.5 High severity
- 8.2 High severity
Recent Unchecked Return Value vulnerabilities
- 9.8 Critical severity
Google Brotli Unchecked Return Value Exploited
- 9.1 Critical severity
- 7.5 High severity
- 7.5 High severity
- 7.8 High severity
- 7.1 High severity
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