HOMEVULNERABILITIESCVE-2019-18277
HIGH

CVE-2019-18277

CWE-444Published: October 23, 2019· Updated: Jun 17, 2026

7.5
CVSS v3.1

Official 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).

NVD Source

Technical Analysis

CVE-2019-18277 can be exploited remotely over the network without requiring physical or adjacent access, significantly expanding the attack surface for threat actors.

The vulnerability requires no privileges and no user interaction, making it a prime target for automated exploitation campaigns and worm-like propagation.

A successful exploit results in full integrity compromise (data manipulation), with a CVSS base score of 7.5.

CVSS v3.1 Vector Breakdown

Exploitability
Attack VectorNetwork
Attack ComplexityLow
Privileges Req.None
User InteractionNone
ScopeUnchanged
Impact
ConfidentialityNone
IntegrityHigh
AvailabilityNone
CVSS:3.1/AV:N/AC:L/PR:N/UI:N/S:U/C:N/I:H/A:N

Affected Vendors & Products

haproxy1 product(s)
haproxy
Source: NVD CPE · 1 total CPE entries

Exploit & PoC Resources

NO KNOWN EXPLOITNo public exploit confirmed at this time
Exploit-DB
Offensive Security exploit database
GitHub PoC Search
Community PoC repositories
Rapid7 / Metasploit
Metasploit module search
PacketStorm
Security advisories & exploits
NVD Detail
Official NIST entry
MITRE CVE
CVE Program entry
External links open in a new tab. Always verify in a controlled environment before use.

Official Patches & Advisories

ADVISORYhttps://nathandavison.com/blog/haproxy-http-request-smuggling
ADVISORYhttps://nathandavison.com/blog/haproxy-http-request-smuggling

All References (14)

→
http://lists.opensuse.org/opensuse-security-announce/2019-12/msg00016.html
→
http://lists.opensuse.org/opensuse-security-announce/2019-12/msg00019.html
→
https://git.haproxy.org/?p=haproxy-2.0.git%3Ba=commit%3Bh=196a7df44d8129d1adc795da020b722614d6a581
→
https://lists.debian.org/debian-lts-announce/2022/05/msg00045.html
→
https://nathandavison.com/blog/haproxy-http-request-smugglingExploit · Third Party Advisory
→
https://usn.ubuntu.com/4174-1/
→
https://www.mail-archive.com/haproxy%40formilux.org/msg34926.html
→
http://lists.opensuse.org/opensuse-security-announce/2019-12/msg00016.html
→
http://lists.opensuse.org/opensuse-security-announce/2019-12/msg00019.html
→
https://git.haproxy.org/?p=haproxy-2.0.git%3Ba=commit%3Bh=196a7df44d8129d1adc795da020b722614d6a581
→
https://lists.debian.org/debian-lts-announce/2022/05/msg00045.html
→
https://nathandavison.com/blog/haproxy-http-request-smugglingExploit · Third Party Advisory
→
https://usn.ubuntu.com/4174-1/
→
https://www.mail-archive.com/haproxy%40formilux.org/msg34926.html

Quick Facts

CVE IDCVE-2019-18277
CVSS Score7.5 / 10
SeverityHIGH
WeaknessCWE-444
CISA KEVNo
Affected1 vendor(s)
PublishedOct 23, 2019

Related CVEs (CWE-444)

CVE-2025-1867
10.0
CVE-2018-3907
10.0
CVE-2025-55315
9.9
CVE-2026-11541
9.8
CVE-2026-1525
9.8
CVE-2015-5739
9.8

Recommended Actions

  • →Apply vendor patches immediately
  • →Monitor CVE-2019-18277 in threat intel feeds
  • →Review IDS/IPS signatures for exploitation attempts
Data sourced from NVD (NIST), CISA KEV, and EPSS (FIRST). Analysis generated by CTIWatch. CVE data is provided under the NVD usage policy.
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