An issue was discovered in Squid 3.x and 4.x through 4.8. It allows attackers to smuggle HTTP requests through frontend software to a Squid instance that splits the HTTP Request pipeline differently. The resulting Response messages corrupt caches (between a client and Squid) with attacker-controlled content at arbitrary URLs. Effects are isolated to software between the attacker client and Squid. There are no effects on Squid itself, nor on any upstream servers. The issue is related to a request header containing whitespace between a header name and a colon.
The product acts as an intermediary HTTP agent (such as a proxy or firewall) in the data flow between two entities such as a client and server, but it does not interpret malformed HTTP requests or responses in ways that are consistent with how the messages will be processed by those entities that are at the ultimate destination.
| Name | Vendor | Start Version | End Version |
|---|---|---|---|
| Squid | Squid-cache | 3.0 (including) | 3.5.28 (including) |
| Squid | Squid-cache | 4.0 (including) | 4.8 (including) |
| Red Hat Enterprise Linux 8 | RedHat | squid:4-8030020200828070549.30b713e6 | * |
| Squid | Ubuntu | devel | * |
| Squid | Ubuntu | disco | * |
| Squid | Ubuntu | eoan | * |
| Squid | Ubuntu | focal | * |
| Squid | Ubuntu | groovy | * |
| Squid | Ubuntu | hirsute | * |
| Squid | Ubuntu | trusty | * |
| Squid | Ubuntu | upstream | * |
| Squid3 | Ubuntu | bionic | * |
| Squid3 | Ubuntu | precise/esm | * |
| Squid3 | Ubuntu | trusty | * |
| Squid3 | Ubuntu | xenial | * |
HTTP requests or responses (“messages”) can be malformed or unexpected in ways that cause web servers or clients to interpret the messages in different ways than intermediary HTTP agents such as load balancers, reverse proxies, web caching proxies, application firewalls, etc. For example, an adversary may be able to add duplicate or different header fields that a client or server might interpret as one set of messages, whereas the intermediary might interpret the same sequence of bytes as a different set of messages. For example, discrepancies can arise in how to handle duplicate headers like two Transfer-encoding (TE) or two Content-length (CL), or the malicious HTTP message will have different headers for TE and CL. The inconsistent parsing and interpretation of messages can allow the adversary to “smuggle” a message to the client/server without the intermediary being aware of it. This weakness is usually the result of the usage of outdated or incompatible HTTP protocol versions in the HTTP agents.