RHSA-2026:27076

Within HostnameError.Error(), when constructing an error string, there is no limit to the number of hosts that will be printed out. Furthermore, the error string is constructed by repeated string concatenation, leading to quadratic runtime. Therefore, a certificate provided by a malicious actor can result in excessive resource consumption.

url.Parse insufficiently validated the host/authority component and accepted some invalid URLs.

During chain building, the amount of work that is done is not correctly limited when a large number of intermediate certificates are passed in VerifyOptions.Intermediates, which can lead to a denial of service. This affects both direct users of crypto/x509 and users of crypto/tls.

Validating certificate chains which use policies is unexpectedly inefficient when certificates in the chain contain a very large number of policy mappings, possibly causing denial of service. This only affects validation of otherwise trusted certificate chains, issued by a root CA in the VerifyOptions.Roots CertPool, or in the system certificate pool.

On Linux, if the target of Root.Chmod is replaced with a symlink while the chmod operation is in progress, Chmod can operate on the target of the symlink, even when the target lies outside the root. The Linux fchmodat syscall silently ignores the AT_SYMLINK_NOFOLLOW flag, which Root.Chmod uses to avoid symlink traversal. Root.Chmod checks its target before acting and returns an error if the target is a symlink lying outside the root, so the impact is limited to cases where the target is replaced with a symlink between the check and operation.

If one side of the TLS connection sends multiple key update messages post-handshake in a single record, the connection can deadlock, causing uncontrolled consumption of resources. This can lead to a denial of service. This only affects TLS 1.3.

gRPC-Go is the Go language implementation of gRPC. Versions prior to 1.79.3 have an authorization bypass resulting from improper input validation of the HTTP/2 `:path` pseudo-header. The gRPC-Go server was too lenient in its routing logic, accepting requests where the `:path` omitted the mandatory leading slash (e.g., `Service/Method` instead of `/Service/Method`). While the server successfully routed these requests to the correct handler, authorization interceptors (including the official `grpc/authz` package) evaluated the raw, non-canonical path string. Consequently, "deny" rules defined using canonical paths (starting with `/`) failed to match the incoming request, allowing it to bypass the policy if a fallback "allow" rule was present. This affects gRPC-Go servers that use path-based authorization interceptors, such as the official RBAC implementation in `google.golang.org/grpc/authz` or custom interceptors relying on `info.FullMethod` or `grpc.Method(ctx)`; AND that have a security policy contains specific "deny" rules for canonical paths but allows other requests by default (a fallback "allow" rule). The vulnerability is exploitable by an attacker who can send raw HTTP/2 frames with malformed `:path` headers directly to the gRPC server. The fix in version 1.79.3 ensures that any request with a `:path` that does not start with a leading slash is immediately rejected with a `codes.Unimplemented` error, preventing it from reaching authorization interceptors or handlers with a non-canonical path string. While upgrading is the most secure and recommended path, users can mitigate the vulnerability using one of the following methods: Use a validating interceptor (recommended mitigation); infrastructure-level normalization; and/or policy hardening.

Pillow is a Python imaging library. Versions 10.3.0 through 12.1.1 did not limit the amount of GZIP-compressed data read when decoding a FITS image, making them vulnerable to decompression bomb attacks. A specially crafted FITS file could cause unbounded memory consumption, leading to denial of service (OOM crash or severe performance degradation). If users are unable to immediately upgrade, they should only open specific image formats, excluding FITS, as a workaround.