Improper input validation in Thumbor
CVE-2026-53503
Thumbor is an open-source photo thumbnail service by globo.com. Prior to 7.8.0, Thumbor's filters:convolution(<matrix>, <columns>, <should_normalize>) filter passes the user-controlled <columns> value to a C extension (thumbor/ext/filters/_convolution.c) where it is used as a divisor (for % and /) 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. This issue is fixed in 7.8.0.
Vulnerability class: Drupalgeddon 2 (CVE-2018-7600)
EPSS: 0.004 (34.7th percentile) — read the EPSS interpretation.
CVSS v3 metric
CVSS v3 base score 7.5 (High). Vector: CVSS:3.1/AV:N/AC:L/PR:N/UI:N/S:U/C:N/I:N/A:H.
Affected products
- Thumbor — versions < 7.8.0
Weakness classification (CWE)
References
- security-advisories@github.com (x_refsource_MISC)
- security-advisories@github.com (x_refsource_MISC)
- security-advisories@github.com (x_refsource_CONFIRM)
Frequently asked questions
- What is CVE-2026-53503?
- CVE-2026-53503 is a high-severity vulnerability in Thumbor, classified under Improper Input Validation. CVSS score: 7.5/10. Published 2026-07-31.
- How severe is CVE-2026-53503?
- High severity. CVSS v3 base score is 7.5 out of 10.