Using go get to fetch a module with the ".git" suffix may unexpectedly fallback to the insecure "git://" protocol if the module is unavailable via the secure "https://" and "git+ssh://" protocols, even if GOINSECURE is not set for said module. This only affects users who are not using the module proxy and are fetching modules directly (i.e. GOPROXY=off).

A malicious HTTP sender can use chunk extensions to cause a receiver reading from a request or response body to read many more bytes from the network than are in the body. A malicious HTTP client can further exploit this to cause a server to automatically read a large amount of data (up to about 1GiB) when a handler fails to read the entire body of a request. Chunk extensions are a little-used HTTP feature which permit including additional metadata in a request or response body sent using the chunked encoding. The net/http chunked encoding reader discards this metadata. A sender can exploit this by inserting a large metadata segment with each byte transferred. The chunk reader now produces an error if the ratio of real body to encoded bytes grows too small.

On Windows, The IsLocal function does not correctly detect reserved device names in some cases. Reserved names followed by spaces, such as "COM1 ", and reserved names "COM" and "LPT" followed by superscript 1, 2, or 3, are incorrectly reported as local. With fix, IsLocal now correctly reports these names as non-local.

The filepath package does not recognize paths with a \??\ prefix as special. On Windows, a path beginning with \??\ is a Root Local Device path equivalent to a path beginning with \\?\. Paths with a \??\ prefix may be used to access arbitrary locations on the system. For example, the path \??\c:\x is equivalent to the more common path c:\x. Before fix, Clean could convert a rooted path such as \a\..\??\b into the root local device path \??\b. Clean will now convert this to .\??\b. Similarly, Join(\, ??, b) could convert a seemingly innocent sequence of path elements into the root local device path \??\b. Join will now convert this to \.\??\b. In addition, with fix, IsAbs now correctly reports paths beginning with \??\ as absolute, and VolumeName correctly reports the \??\ prefix as a volume name. UPDATE: Go 1.20.11 and Go 1.21.4 inadvertently changed the definition of the volume name in Windows paths starting with \?, resulting in filepath.Clean(\?\c:) returning \?\c: rather than \?\c:\ (among other effects). The previous behavior has been restored.

A malicious HTTP/2 client which rapidly creates requests and immediately resets them can cause excessive server resource consumption. While the total number of requests is bounded by the http2.Server.MaxConcurrentStreams setting, resetting an in-progress request allows the attacker to create a new request while the existing one is still executing. With the fix applied, HTTP/2 servers now bound the number of simultaneously executing handler goroutines to the stream concurrency limit (MaxConcurrentStreams). New requests arriving when at the limit (which can only happen after the client has reset an existing, in-flight request) will be queued until a handler exits. If the request queue grows too large, the server will terminate the connection. This issue is also fixed in golang.org/x/net/http2 for users manually configuring HTTP/2. The default stream concurrency limit is 250 streams (requests) per HTTP/2 connection. This value may be adjusted using the golang.org/x/net/http2 package; see the Server.MaxConcurrentStreams setting and the ConfigureServer function.

The HTTP/2 protocol allows a denial of service (server resource consumption) because request cancellation can reset many streams quickly, as exploited in the wild in August through October 2023.

Line directives ("//line") can be used to bypass the restrictions on "//go:cgo_" directives, allowing blocked linker and compiler flags to be passed during compilation. This can result in unexpected execution of arbitrary code when running "go build". The line directive requires the absolute path of the file in which the directive lives, which makes exploiting this issue significantly more complex.

QUIC connections do not set an upper bound on the amount of data buffered when reading post-handshake messages, allowing a malicious QUIC connection to cause unbounded memory growth. With fix, connections now consistently reject messages larger than 65KiB in size.

Processing an incomplete post-handshake message for a QUIC connection can cause a panic.

The go.mod toolchain directive, introduced in Go 1.21, can be leveraged to execute scripts and binaries relative to the root of the module when the "go" command was executed within the module. This applies to modules downloaded using the "go" command from the module proxy, as well as modules downloaded directly using VCS software.

The html/template package does not apply the proper rules for handling occurrences of "<script", "<!--", and "</script" within JS literals in <script> contexts. This may cause the template parser to improperly consider script contexts to be terminated early, causing actions to be improperly escaped. This could be leveraged to perform an XSS attack.

The html/template package does not properly handle HTML-like "" comment tokens, nor hashbang "#!" comment tokens, in <script> contexts. This may cause the template parser to improperly interpret the contents of <script> contexts, causing actions to be improperly escaped. This may be leveraged to perform an XSS attack.