CVE-2021-40346
An integer overflow exists in HAProxy 2.0 through 2.5 in htx_add_header that can be exploited to perform an HTTP request smuggling attack, allowing an attacker to bypass all configured http-request HAProxy ACLs and possibly other ACLs.
Does this matter?
EPSS puts the probability of exploitation in the next 30 days at 58.8%, higher than 99% of all known CVEs. Patch or mitigate before the next change window.
Description
An integer overflow exists in HAProxy 2.0 through 2.5 in htx_add_header that can be exploited to perform an HTTP request smuggling attack, allowing an attacker to bypass all configured http-request HAProxy ACLs and possibly other ACLs.
- CVSS 3.1
- 7.5 HIGHCVSS:3.1/AV:N/AC:L/PR:N/UI:N/S:U/C:N/I:H/A:N
- EPSS
- 58.83% probability · 99th percentile
- Public exploits
- None in Exploit-DB
- CISA KEV
- Not listed
- Weakness
- CWE-190
- Affected
- haproxy/haproxy · debian/debian linux · fedoraproject/fedora
- Source
- cve@mitre.org
EPSS 58.8% since 3 November 2026; no change recorded yet. The dashed line is the ten per cent mark our analysts treat as “patch before the next change window”. Points are recorded when the score first appears and whenever it moves by a percentage point or more.
References
- https://git.haproxy.org/?p=haproxy.gitPatch, Vendor Advisory
- https://github.com/haproxy/haproxy/commit/3b69886f7dcc3cfb3d166309018e6cfec9ce2c95Patch, Third Party Advisory
- https://jfrog.com/blog/critical-vulnerability-in-haproxy-cve-2021-40346-integer-overflow-enables-http-smuggling/Exploit, Mitigation, Third Party Advisory
- https://lists.apache.org/thread.html/r284567dd7523f5823e2ce995f787ccd37b1cc4108779c50a97c79120%40%3Cdev.cloudstack.apache.org%3E
- https://lists.apache.org/thread.html/r8a58fd7a29808e5d27ee56877745e58dc4bb041b9af94601554e2a5a%40%3Cdev.cloudstack.apache.org%3E
- https://lists.fedoraproject.org/archives/list/package-announce%40lists.fedoraproject.org/message/A7V2IYO22LWVBGUNZWVKNTMDV4KINLFO/
- https://lists.fedoraproject.org/archives/list/package-announce%40lists.fedoraproject.org/message/MXTSBY2TEAXWZVFQM3CXHJFRONX7PEMN/
- https://www.debian.org/security/2021/dsa-4968Third Party Advisory
- https://www.mail-archive.com/haproxy%40formilux.org
- https://www.mail-archive.com/haproxy%40formilux.org/msg41114.html
- https://git.haproxy.org/?p=haproxy.gitPatch, Vendor Advisory
- https://github.com/haproxy/haproxy/commit/3b69886f7dcc3cfb3d166309018e6cfec9ce2c95Patch, Third Party Advisory
- https://jfrog.com/blog/critical-vulnerability-in-haproxy-cve-2021-40346-integer-overflow-enables-http-smuggling/Exploit, Mitigation, Third Party Advisory
- https://lists.apache.org/thread.html/r284567dd7523f5823e2ce995f787ccd37b1cc4108779c50a97c79120%40%3Cdev.cloudstack.apache.org%3E
- https://lists.apache.org/thread.html/r8a58fd7a29808e5d27ee56877745e58dc4bb041b9af94601554e2a5a%40%3Cdev.cloudstack.apache.org%3E
- https://lists.fedoraproject.org/archives/list/package-announce%40lists.fedoraproject.org/message/A7V2IYO22LWVBGUNZWVKNTMDV4KINLFO/
- https://lists.fedoraproject.org/archives/list/package-announce%40lists.fedoraproject.org/message/MXTSBY2TEAXWZVFQM3CXHJFRONX7PEMN/
- https://www.debian.org/security/2021/dsa-4968Third Party Advisory
- https://www.mail-archive.com/haproxy%40formilux.org
- https://www.mail-archive.com/haproxy%40formilux.org/msg41114.html
Source: NVD record, EPSS from FIRST.org, KEV from CISA, exploits from Exploit-DB. Refreshed daily. Download this record as JSON.