CVE-2019-18277
CVSS v3
7.5
HIGH
EPSS Score
10.0 %
exploit probability, as of 2026-09-25
CISA KEV
No
known exploited
Exploitation
—
SSVC status
Description
A flaw was found in HAProxy before 2.0.6. In legacy mode, messages featuring a transfer-encoding header missing the "chunked" value were not being correctly rejected. The impact was limited but if combined with the "http-reuse always" setting, it could be used to help construct an HTTP request smuggling attack against a vulnerable component employing a lenient parser that would ignore the content-length header as soon as it saw a transfer-encoding one (even if not entirely valid according to the specification).
Technical details
- Published
- 2019-10-23
Frequently asked questions
What is CVE-2019-18277?
A flaw was found in HAProxy before 2.0.6. In legacy mode, messages featuring a transfer-encoding header missing the "chunked" value were not being correctly rejected. The impact was limited but if combined with the "http-reuse always" setting, it could be used to help construct an HTTP request smuggling attack against a vulnerable component employing a lenient parser that would ignore the content-length header as soon as it saw a transfer-encoding one (even if not entirely valid according to the specification).
Is CVE-2019-18277 actively exploited?
Active exploitation of CVE-2019-18277 has not been confirmed. Its EPSS score was 10.0% on 2026-09-25, the estimated probability of exploitation in the next 30 days.
What is the CVSS score for CVE-2019-18277?
CVE-2019-18277 has a CVSS v3 base score of 7.5 (HIGH severity).
Is CVE-2019-18277 affecting your environment?
Use isMalicious to check if any of your IPs or domains are associated with this vulnerability's IOCs.
No credit card required · 500 free checks/month · Free API key
Other 2019 vulnerabilities worth triaging
Ranked by exploit probability (EPSS).