CVE-2019-16785 HTTP Request Smuggling: LF vs CRLF handling in Waitress

2019-12-2023:00:25

CWE-444

GitHub_M

www.cve.org

7.1 High

CVSS3

Attack Vector

NETWORK

Attack Complexity

HIGH

Privileges Required

LOW

User Interaction

NONE

Scope

CHANGED

Confidentiality Impact

HIGH

Integrity Impact

LOW

Availability Impact

NONE

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

7.4 High

AI Score

Confidence

High

0.021 Low

EPSS

Percentile

89.1%

JSON

Waitress through version 1.3.1 implemented a “MAY” part of the RFC7230 which states: “Although the line terminator for the start-line and header fields is the sequence CRLF, a recipient MAY recognize a single LF as a line terminator and ignore any preceding CR.” Unfortunately if a front-end server does not parse header fields with an LF the same way as it does those with a CRLF it can lead to the front-end and the back-end server parsing the same HTTP message in two different ways. This can lead to a potential for HTTP request smuggling/splitting whereby Waitress may see two requests while the front-end server only sees a single HTTP message. This issue is fixed in Waitress 1.4.0.

CNA Affected

[
  {
    "product": "Waitress",
    "vendor": "Pylons",
    "versions": [
      {
        "lessThanOrEqual": "1.3.1",
        "status": "affected",
        "version": "<= 1.3.1",
        "versionType": "custom"
      }
    ]
  }
]