HTTP request smuggling in Varnish Cache
| Risk | Medium |
| Patch available | YES |
| Number of vulnerabilities | 1 |
| CVE-ID | CVE-2021-36740 |
| CWE-ID | CWE-444 |
| Exploitation vector | Network |
| Public exploit | N/A |
| Vulnerable software Subscribe |
Varnish Cache Server applications / IDS/IPS systems, Firewalls and proxy servers |
| Vendor | Varnish Software |
Security Bulletin
This security bulletin contains one medium risk vulnerability.
1) Inconsistent interpretation of HTTP requests
EUVDB-ID: #VU55501
Risk: Medium
CVSSv3.1: 6.3 [CVSS:3.1/AV:N/AC:L/PR:N/UI:N/S:C/C:L/I:L/A:N/E:U/RL:O/RC:C]
CVE-ID: CVE-2021-36740
CWE-ID:
CWE-444 - Inconsistent Interpretation of HTTP Requests ('HTTP Request Smuggling')
Exploit availability: No
DescriptionThe vulnerability allows a remote attacker to preform HTTP request smuggling attacks.
The vulnerability exists due to improper validation of HTTP/2 requests. A remote attacker can send a specially crafted HTTP/2 POST request with a large Content-Length header to the server and smuggle arbitrary HTTP headers.
Successful exploitation of vulnerability may allow an attacker to poison HTTP cache or bypass VCL authorization.
MitigationInstall updates from vendor's website.
Vulnerable software versionsVarnish Cache: 6.0.0 - 6.6.0
External linkshttp://github.com/varnishcache/varnish-cache/commit/82b0a629f60136e76112c6f2c6372cce77b683be
http://github.com/varnishcache/varnish-cache/commit/9be22198e258d0e7a5c41f4291792214a29405cf
http://docs.varnish-software.com/security/VSV00007/
http://varnish-cache.org/security/VSV00007.html
Q & A
Can this vulnerability be exploited remotely?
Yes. This vulnerability can be exploited by a remote non-authenticated attacker via the Internet.
How the attacker can exploit this vulnerability?
The attacker would have to send a specially crafted request to the affected application in order to exploit this vulnerability.
Is there known malware, which exploits this vulnerability?
No. We are not aware of malware exploiting this vulnerability.
