CVE-2019-12520
Status: ModifiedHigh (7.5)—
An issue was discovered in Squid through 4.7 and 5. When receiving a request, Squid checks its cache to see if it can serve up a response. It does this by making a MD5 hash of the absolute URL of the request. If found, it servers the request. The absolute URL can include the decoded UserInfo (username and password) for certain protocols. This decoded info is prepended to the domain. This allows an attacker to provide a username that has special characters to delimit the domain, and treat the rest of the URL as a path or query string.
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An attacker could first make a request to their domain using an encoded username, then when a request for the target domain comes in that decodes to the exact URL, it will serve the attacker's HTML instead of the real HTML. On Squid servers that also act as reverse proxies, this allows an attacker to gain access to features that only reverse proxies can use, such as ESI.
CVSS
- Version: 3.1
- Vector: CVSS:3.1/AV:N/AC:L/PR:N/UI:N/S:U/C:H/I:N/A:N
- Base score: 7.5
Exploitation probability (EPSS)
- Probability of exploitation in the next 30 days: 3.92%
- Percentile among all scored CVEs: 90
- Score date: 10/6/2026
EPSS (Exploit Prediction Scoring System, FIRST) estimates how likely a vulnerability is to be exploited in the wild within 30 days. It complements CVSS (impact) and CISA KEV (confirmed exploitation).
Affected technologies (3)
CWEs
- CWE-20
References
- http://www.squid-cache.org/Versions/v4/
- http://www.squid-cache.org/Versions/v4/changesets/
- https://github.com/squid-cache/squid/commits/v4
- https://gitlab.com/jeriko.one/security/-/blob/master/squid/CVEs/CVE-2019-12520.txt
- https://lists.debian.org/debian-lts-announce/2020/07/msg00009.html
- https://security.netapp.com/advisory/ntap-20210205-0006/
- https://usn.ubuntu.com/4446-1/
- https://www.debian.org/security/2020/dsa-4682
- http://www.squid-cache.org/Versions/v4/
- http://www.squid-cache.org/Versions/v4/changesets/
- https://github.com/squid-cache/squid/commits/v4
- https://gitlab.com/jeriko.one/security/-/blob/master/squid/CVEs/CVE-2019-12520.txt
- https://lists.debian.org/debian-lts-announce/2020/07/msg00009.html
- https://security.netapp.com/advisory/ntap-20210205-0006/
- https://usn.ubuntu.com/4446-1/
- https://www.debian.org/security/2020/dsa-4682
Raw JSON (NVD)
Show
{
"id": "CVE-2019-12520",
"cveTags": [],
"metrics": {
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"vectorString": "AV:N/AC:L/Au:N/C:P/I:N/A:N",
"authentication": "NONE",
"integrityImpact": "NONE",
"accessComplexity": "LOW",
"availabilityImpact": "NONE",
"confidentialityImpact": "PARTIAL"
},
"acInsufInfo": false,
"impactScore": 2.9,
"baseSeverity": "MEDIUM",
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"impactScore": 3.6,
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"affected": [
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"weaknesses": [
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"description": [
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"value": "An issue was discovered in Squid through 4.7 and 5. When receiving a request, Squid checks its cache to see if it can serve up a response. It does this by making a MD5 hash of the absolute URL of the request. If found, it servers the request. The absolute URL can include the decoded UserInfo (username and password) for certain protocols. This decoded info is prepended to the domain. This allows an attacker to provide a username that has special characters to delimit the domain, and treat the rest of the URL as a path or query string. An attacker could first make a request to their domain using an encoded username, then when a request for the target domain comes in that decodes to the exact URL, it will serve the attacker's HTML instead of the real HTML. On Squid servers that also act as reverse proxies, this allows an attacker to gain access to features that only reverse proxies can use, such as ESI."
},
{
"lang": "es",
"value": "Se descubrió un problema en Squid versiones hasta 4.7 y 5. Cuando se recibe una petición, Squid comprueba su memoria caché para visualizar si puede servir una respuesta. Lo hace al realizar un hash MD5 de la URL absoluta de la petición. Si se encuentra, sirve la petición. La URL absoluta puede incluir la UserInfo decodificada (nombre de usuario y contraseña) para determinados protocolos. Esta información decodificada se antepone al dominio. Esto permite a un atacante proporcionar un nombre de usuario que tenga caracteres especiales para delimitar el dominio y tratar el resto de la URL como una ruta o cadena de consulta. Un atacante podría primero hacer una petición a su dominio usando un nombre de usuario codificado, luego, cuando llega una petición para el dominio objetivo que decodifica a la URL exacta, servirá el HTML del atacante en lugar del HTML real. En los servidores de Squid que también actúan como proxies inversos, esto permite a un atacante conseguir acceso a funcionalidades que solo los proxies inversos pueden utilizar, tal y como ESI."
}
],
"lastModified": "2026-06-17T02:14:48.620",
"configurations": [
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