Squid is an open source caching proxy for the Web supporting HTTP, HTTPS, FTP, and more. Due to Input Validation, Premature Release of Resource During Expected Lifetime, and Missing Release of Resource after Effective Lifetime bugs, Squid is vulnerable to Denial of Service attacks by a trusted server against all clients using the proxy. This bug is fixed in the default build configuration of Squid version 6.10.

Squid is a caching proxy for the Web supporting HTTP, HTTPS, FTP, and more. Due to an Out-of-bounds Write error when assigning ESI variables, Squid is susceptible to a Memory Corruption error. This error can lead to a Denial of Service attack.

References: https://github.com/squid-cache/squid/security/advisories/GHSA-wgvf-q977-9xjg https://megamansec.github.io/Squid-Security-Audit/esi-underflow.html

Upstream patch: https://github.com/squid-cache/squid/commit/f411fe7d75197852f0e5ee85027a06d58dd8df4c.patch

Last updated 28 February 2025

Last updated 24 July 2024

Last updated 24 July 2024

Last updated 24 July 2024

Last updated 24 July 2024

Squid is a caching proxy for the Web supporting HTTP, HTTPS, FTP, and more. Due to a NULL pointer dereference bug Squid is vulnerable to a Denial of Service attack against Squid's Gopher gateway. The gopher protocol is always available and enabled in Squid prior to Squid 6.0.1. Responses triggering this bug are possible to be received from any gopher server, even those without malicious intent. Gopher support has been removed in Squid version 6.0.1. Users are advised to upgrade. Users unable to upgrade should reject all gopher URL requests.

Squid is a caching proxy for the Web. Due to an Improper Validation of Specified Index bug, Squid versions 3.3.0.1 through 5.9 and 6.0 prior to 6.4 compiled using --with-openssl are vulnerable to a Denial of Service attack against SSL Certificate validation. This problem allows a remote server to perform Denial of Service against Squid Proxy by initiating a TLS Handshake with a specially crafted SSL Certificate in a server certificate chain. This attack is limited to HTTPS and SSL-Bump. This bug is fixed in Squid version 6.4. In addition, patches addressing this problem for the stable releases can be found in Squid's patch archives. Those who you use a prepackaged version of Squid should refer to the package vendor for availability information on updated packages.

Some reference updates.

On 11/10/23 20:55, Joshua Rogers wrote: The issues are listed below. Due to the sheer size of issues discovered, technical details are not included in this email. However, breakdowns of the code and proof-of-concepts can be found on GitHub: https://megamansec.github.io/Squid-Security-Audit/

Cache Poisoning by Large Stored Response Headers (With Bonus XSS) ... GHSA-543m-w2m2-g255 Gopher Assertion Crash ... GHSA-f5cp-6rh3-284w Assertion in Gopher Response Handling ... CVE-2021-46784 / GHSA-f5cp-6rh3-284w

AYJ

An issue was discovered in Squid 4.9 through 4.17 and 5.0.6 through 5.6. Due to inconsistent handling of internal URIs, there can be Exposure of Sensitive Information about clients using the proxy via an HTTPS request to an internal cache manager URL. This is fixed in 5.7.

A buffer over-read was discovered in libntlmauth in Squid 2.5 through 5.6. Due to incorrect integer-overflow protection, the SSPI and SMB authentication helpers are vulnerable to reading unintended memory locations. In some configurations, cleartext credentials from these locations are sent to a client. This is fixed in 5.7.

An issue was discovered in Squid 5.0.6 through 5.1.x before 5.2. When validating an origin server or peer certificate, Squid may incorrectly classify certain certificates as trusted. This problem allows a remote server to obtain security trust well improperly. This indication of trust may be passed along to clients, allowing access to unsafe or hijacked services.

An issue was discovered in Squid before 4.15 and 5.x before 5.0.6. Due to an input-validation bug, it is vulnerable to a Denial of Service attack (against all clients using the proxy). A client sends an HTTP Range request to trigger this.

An issue was discovered in Squid before 4.15 and 5.x before 5.0.6. Due to a memory-management bug, it is vulnerable to a Denial of Service attack (against all clients using the proxy) via HTTP Range request processing.

An issue was discovered in Squid before 4.15 and 5.x before 5.0.6. An integer overflow problem allows a remote server to achieve Denial of Service when delivering responses to HTTP Range requests. The issue trigger is a header that can be expected to exist in HTTP traffic without any malicious intent.

An issue was discovered in Squid 4.x before 4.15 and 5.x before 5.0.6. If a remote server sends a certain response header over HTTP or HTTPS, there is a denial of service. This header can plausibly occur in benign network traffic.

An issue was discovered in Squid before 4.15 and 5.x before 5.0.6. Due to incorrect parser validation, it allows a Denial of Service attack against the Cache Manager API. This allows a trusted client to trigger memory leaks that. over time, lead to a Denial of Service via an unspecified short query string. This attack is limited to clients with Cache Manager API access privilege.

An issue was discovered in Squid before 4.15 and 5.x before 5.0.6. Due to a buffer-management bug, it allows a denial of service. When resolving a request with the urn: scheme, the parser leaks a small amount of memory. However, there is an unspecified attack methodology that can easily trigger a large amount of memory consumption.

Due to an input validation bug Squid is vulnerable to a Denial of Service against all clients using the proxy. This problem allows a remote server to perform Denial of Service when delivering HTTP Response messages. The issue trigger is a header which can be expected to exist in HTTP traffic without any malicious intent by the server.

Reference: https://github.com/squid-cache/squid/security/advisories/GHSA-572g-rvwr-6c7f/

An issue was discovered in Squid through 4.13 and 5.x through 5.0.4. Due to improper input validation, it allows a trusted client to perform HTTP Request Smuggling and access services otherwise forbidden by the security controls. This occurs for certain uriwhitespace configuration settings.

Squid through 4.14 and 5.x through 5.0.5, in some configurations, allows information disclosure because of an out-of-bounds read in WCCP protocol data. This can be leveraged as part of a chain for remote code execution as nobody.

An issue was discovered in Squid before 4.12 and 5.x before 5.0.3. Due to use of a potentially dangerous function, Squid and the default certificate validation helper are vulnerable to a Denial of Service when opening a TLS connection to an attacker-controlled server for HTTPS. This occurs because unrecognized error values are mapped to NULL, but later code expects that each error value is mapped to a valid error string.

An issue was discovered in Squid 5.x before 5.0.3. Due to an Incorrect Synchronization, a Denial of Service can occur when processing objects in an SMP cache because of an Ipc::Mem::PageStack::pop ABA problem during access to the memory page/slot management list.

An issue was discovered in Squid through 4.7. When Squid is run as root, it spawns its child processes as a lesser user, by default the user nobody. This is done via the leavesuid call. leavesuid leaves the Saved UID as 0. This makes it trivial for an attacker who has compromised the child process to escalate their privileges back to root.

A vulnerability was found in cachemgr.cgi web module of Squid through 4.7 has XSS via the username or auth parameter.

Reference: https://bugs.squid-cache.org/showbug.cgi?id=4957 https://github.com/squid-cache/squid/pull/429

This vulnerability allows remote attackers to deny service on vulnerable installations of The Squid Software Foundation Squid 3.5.27-20180318. Authentication is not required to exploit this vulnerability. The specific flaw exists within ClientRequestContext::sslBumpAccessCheck(). A crafted request can trigger the dereference of a null pointer. An attacker can leverage this vulnerability to create a denial-of-service condition to users of the system. Was ZDI-CAN-6088.

Double free vulnerability in Esi.cc in Squid 3.x before 3.5.18 and 4.x before 4.0.10 allows remote servers to cause a denial of service (crash) via a crafted Edge Side Includes (ESI) response.

Due to incorrect reference counting Squid is vulnerable to a denial of service attack when processing ESI responses.

External references:

http://www.squid-cache.org/Advisories/SQUID-20169.txt

Upstream fixes:

Squid 3.5:

http://www.squid-cache.org/Versions/v3/3.5/changesets/SQUID-20169.patch

Squid 3.4:

http://www.squid-cache.org/Versions/v3/3.4/changesets/SQUID-20169.patch

NOTE: For the other related CVE, CVE-2016-4555, see Bug 1334246

clientsiderequest.cc in Squid 3.x before 3.5.18 and 4.x before 4.0.10 allows remote servers to cause a denial of service (crash) via crafted Edge Side Includes (ESI) responses.