CVE-2020-5255
LOWDescription
In Symfony before versions 4.4.7 and 5.0.7, when a `Response` does not contain a `Content-Type` header, affected versions of Symfony can fallback to the format defined in the `Accept` header of the request, leading to a possible mismatch between the response's content and `Content-Type` header. When the response is cached, this can prevent the use of the website by other users. This has been patched in versions 4.4.7 and 5.0.7.
How to fix
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Remediation is compiled from vendor and distribution security advisories. Always confirm against the linked source for your exact version and platform.
CVSS v3 Vector
Exploitability
Impact
CVSS:3.1/AV:N/AC:H/PR:L/UI:R/S:U/C:N/I:N/A:L
Exploit Intelligence
Moderate risk: more likely to be exploited than 69% of all known CVEs.
References
Related Vulnerabilities
Other CWE-435 vulnerabilities, ordered by exploit likelihood. View all
| CVE | Severity | CVSS | EPSS | Exploited | Fix |
|---|---|---|---|---|---|
| CVE-2021-34699 | High | 7.7 | 1.2% | - | - |
| CVE-2023-43052 | Medium | 5.3 | 0.4% | - | - |
Common questions
How do I fix CVE-2020-5255?
Upgrade symfony on debian 12 to 4.4.8-1 or later.
Is CVE-2020-5255 being actively exploited?
Not that we know of. CVE-2020-5255 is not in the CISA Known Exploited Vulnerabilities catalog. Its EPSS score of 1.3% is the estimated probability that it will be exploited in the next 30 days. That is higher than 69% of all scored CVEs.
How severe is CVE-2020-5255?
CVE-2020-5255 has a CVSS v3 base score of 2.6, rated low. CVSS rates the technical impact if the vulnerability is exploited, not how likely that is, so weigh it alongside the exploit-prediction score when you decide what to patch first.
What does CVE-2020-5255 affect?
Published advisories record a fix for symfony (Debian). Only products with a sourced advisory are listed, so treat this as what we can cite rather than a complete inventory.
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Markdown
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This product uses NVD data but is not endorsed or certified by the NVD. EPSS scores courtesy of FIRST.org (https://www.first.org/epss). Source: CISA KEV Catalog. Data as of 2026-06-17.