# CVE-2026-53503: Thumbor convolution filter allows divide-by-zero in C extension leading to remote DoS > Remote attackers can crash the Thumbor service by sending a convolution filter request with zero columns, causing a divide-by-zero error. - **Severity:** High 7.5 (`CVSS:3.1/AV:N/AC:L/PR:N/UI:N/S:U/C:N/I:N/A:H`) - **Exploited in the wild:** Not known - **Login needed:** Not needed - **Attackable:** Over the internet - **Victim action needed:** Not needed - **Fix available:** Yes - **Published:** 31 Jul 2026 - **Updated:** 31 Jul 2026 - **Also known as:** DEBIAN-CVE-2026-53503, GHSA-cqjp-jf4r-h5q9, PYSEC-2026-3619, UBUNTU-CVE-2026-53503 ## What is CVE-2026-53503? CVE-2026-53503 is a high-severity denial of service vulnerability in thumbor, published on 31 Jul 2026. An attacker can exploit it over the internet without logging in, with no action from the victim. ### Official description Thumbor is an open-source photo thumbnail service by globo.com. Prior to 7.8.0, Thumbor's filters:convolution(, , ) filter passes the user-controlled 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. Weakness: CWE-369 (Divide By Zero), CWE-20 (Improper Input Validation) ## Which versions are affected by CVE-2026-53503? 3 open source packages ship an affected version, including thumbor. | Package | Ecosystem | Affected | Fixed in | | --- | --- | --- | --- | | `thumbor` | PyPI | All versions | 7.8.0 | | `thumbor` | PyPI | All versions | 7.8.0 | | `thumbor` | PyPI | All versions | 7.8.0 | ## How do I fix CVE-2026-53503? Upgrade thumbor to 7.8.0 or later. ## Is CVE-2026-53503 being exploited? It is not confirmed as exploited in the wild, but public exploit code for CVE-2026-53503 exists. ## Fix prompt for AI coding agents ```text Check this codebase for CVE-2026-53503 and fix it if it is affected. What it is: CVE-2026-53503 is a high-severity denial of service vulnerability in thumbor, published on 31 Jul 2026. An attacker can exploit it over the internet without logging in, with no action from the victim. Exploitation: It is not confirmed as exploited in the wild, but public exploit code for CVE-2026-53503 exists. Affected packages and fixed versions: - thumbor (PyPI): affected all versions; fixed in 7.8.0 - thumbor (PyPI): affected all versions; fixed in 7.8.0 - thumbor (PyPI): affected all versions; fixed in 7.8.0 Task: 1. Search the dependency manifests and lockfiles (for example package.json, package-lock.json, requirements.txt, poetry.lock, uv.lock, pom.xml, build.gradle, go.mod, Cargo.lock, Gemfile.lock) and any Dockerfiles for the affected packages, including transitive dependencies. 2. If an affected version is in use, upgrade it to the fixed version for its release line with the project's package manager, so the lockfile is regenerated. Prefer the smallest upgrade that fixes it. 3. If there is no fix, or the upgrade would break the build, do not guess: explain the risk and the safest workaround instead. 4. Run the tests and summarise what changed and why. 5. If nothing in the project is affected, say so and change nothing. Reference: https://insights.sbomify.com/CVE-2026-53503/ (Markdown: https://insights.sbomify.com/CVE-2026-53503/index.md) ``` ## Sources - CVE record: https://www.cve.org/CVERecord?id=CVE-2026-53503 - NVD: https://nvd.nist.gov/vuln/detail/CVE-2026-53503 - OSV: https://osv.dev/vulnerability/CVE-2026-53503 --- From sbomify Insights: https://insights.sbomify.com/CVE-2026-53503/ Summaries are generated and may contain mistakes; the official description above is the record.