CVE-2020-5255Network attack vector

Cache poisoning via Accept header fallback

Published Mar 30, 2020 · Updated Aug 4, 2024

Improper input validation in Symfony 4.4.0 through 4.4.6 and 5.0.0 through 5.0.6 allows attackers to disrupt cached websites. HttpFoundation uses a request Accept header to infer Content-Type when a Response omits that header, allowing content and metadata to diverge in a cache. Remote attackers must reach an application route that produces such responses and a shared cache; poisoned entries can prevent subsequent users from using the website without exposing or modifying stored data.

CVSS severity4.3
Medium
EPSS probability1.30%
Next 30 days · Sep 16, 2026
Known exploitationUnconfirmed
Based on sourced intelligence
Hinoki checkNot available
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Summary

What happened

Improper input validation in Symfony 4.4.0 through 4.4.6 and 5.0.0 through 5.0.6 allows attackers to disrupt cached websites. HttpFoundation uses a request Accept header to infer Content-Type when a Response omits that header, allowing content and metadata to diverge in a cache. Remote attackers must reach an application route that produces such responses and a shared cache; poisoned entries can prevent subsequent users from using the website without exposing or modifying stored data.

The record

CVE
CVE-2020-5255
Published
Mar 30, 2020
Updated
Aug 4, 2024
Vendor
Symfony
Product
Symfony
Classifications
CWE-435, CWE-20
Attack vector
network
Privileges
authenticated

Timeline

How it unfolded

  1. Mar 30, 2020CVE publishedPublication date reported by the CVE source.
  2. Aug 4, 2024Record updatedLatest update available in the CVE record.

Exploitability

Present is not the same as exploitable

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Is a vulnerable build present?

Compare these published version ranges with your installed build and any vendor patches.

  1. Affected versionversion=>= 4.4.0 and < 4.4.7
  2. Affected versionversion=>= 5.0.0 and < 5.0.7

What conditions does exploitation require?

Attack vectornetwork
Required privilegesauthenticated

What is affected?

Symfony · Symfonyversion=>= 4.4.0 and < 4.4.7; version=>= 5.0.0 and < 5.0.7

Published CVSS scores

4.3NVDCVSS:3.1/AV:N/AC:L/PR:L/UI:N/S:U/C:N/I:N/A:L
4.0NVDAV:N/AC:L/Au:S/C:N/I:N/A:P
2.6GitHubCVSS:3.1/AV:N/AC:H/PR:L/UI:R/S:U/C:N/I:N/A:L

CVSS describes severity. EPSS estimates exploitation probability.

Attacks

What attackers are doing with it

Daily unique IPs observed by Shadowserver honeypots for known exploited vulnerabilities (KEVs). Missing observations do not establish an absence of attacks.

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No observations available

Sep 10, 2026Sep 16, 2026
Latest reporting daySep 16, 2026
Latest daily unique IPsUnavailable
Prior 30-day averageUnavailable
SourceShadowserver honeypots (KEV)
Vectornetwork
Privilegesauthenticated
Known exploitationUnconfirmed
Public exploitUnconfirmed

Weakness, pattern, technique

CWE-435Improper Interaction Between Multiple Correctly-Behaving Entities
CWE-20Improper Input Validation

Public exploit references

No public exploit references are available in this record.

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Technologies

Your stack

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Your stack

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