What’s Vulnerable › Vulnerabilities

CVE-2026-53503: Thumbor convolution filter allows divide-by-zero in C extension leading to remote DoS

• Severity: high (CVSS 7.5 v3.1)
• Exploited in the wild: not listed in CISA KEV
• EPSS: 0.8% probability of exploitation in the next 30 days
• Public exploit or detection template: none known
• Published: 2026-07-31 · updated 2026-09-08
• Weakness: CWE-20

Description

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.

Affected products

• thumbor: before 7.8.0

References

• https://github.com/thumbor/thumbor/commit/447e192e3fb92e64c12e5354a56a4a7133f69d73
• https://github.com/thumbor/thumbor/releases/tag/7.8.0
• https://github.com/thumbor/thumbor/security/advisories/GHSA-cqjp-jf4r-h5q9
• https://github.com/thumbor/thumbor/security/advisories/GHSA-cqjp-jf4r-h5q9

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