CVE-2026-53502

Thumbor before 7.8.0 in the filters:proportion(<value>) filter does not enforce an upper bound on <value> and runs in the post-transform phase. An attacker can trigger extremely large resizes (CPU/memory exhaustion) and cause denial of service.

Thumbor before 7.8.0 in the convolution filter uses a regular expression that performs exponential backtracking on crafted repeated numeric input, allowing a URL request to exhaust processing time.

Thumbor before 7.8.0 in the filters:convolution(<matrix>, <columns>, <should_normalize>) filter passes the user-controlled <columns> value to a C extension where it is used as a divisor without validating columns > 0. When columns=0, the C code triggers undefined behavior; on x86_64 this reliably results in a fatal divide-by-zero trap (SIGFPE) and crashes the Thumbor process, causing a remote denial of service.

Thumbor before 7.8.0 in HMAC validation uses Python's .replace() to remove the signature from the URL before validation. Since .replace() removes all occurrences of the substring, an attacker can insert the same signature multiple times in the URL and manipulate the final URL used for validation, enabling loading images from unintended domains or paths.

Thumbor before 7.8.0 in the ALLOWED_SOURCES configuration passes plain strings to re.match() without escaping dots, so a hostname differing at dot positions can match the allowlist.