CVE-2026-47729
Description
A flaw was found in Squid. Due to improper input validation, an out-of-bounds read can occur in the FTP gateway. This issue allows an authenticated and trusted client to read memory from random transactions when accessing a misbehaving FTP server using the Squid gateway feature.
Statement
To exploit this issue, an attacker must have a valid account on the Squid proxy and must also control an FTP server reachable from the proxy on port 21. HTTPS traffic handled via CONNECT tunnels (the vast majority of modern web traffic) is opaque to the proxy because the underlying request data is encrypted and Squid does not have access to it. The impact is limited to information disclosure of cleartext HTTP request contents or traffic in TLS-terminating (SSL bump) proxy configurations where Squid decrypts and inspects traffic. FTP protocol usage has declined considerably in most environments since major browsers removed FTP support, further narrowing the practical attack surface. Due to these reasons, this vulnerability has been rated with a moderate severity.
Mitigation
When FTP access is not required, block FTP traffic at the proxy by adding the following settings to the squid.conf configuration file above any custom 'http_access allow' rules:
acl FTP proto FTP
http_access deny FTP
When FTP access is required, configure Squid to only allow FTP access to specific and trusted destination domains. See the example below for restricting FTP access to the 'trusted.server.example.com' domain:
acl FTP proto FTP
acl ftp_allowlist dstdomain .trusted.server.example.com
http_access deny FTP !ftp_allowlist
Common Vulnerability Scoring System (CVSS) Score Details
Info alert:Important note
CVSS scores for open source components depend on vendor-specific factors (e.g. version or build chain). Therefore, Red Hat's score and impact rating can be different from NVD and other vendors. Red Hat remains the authoritative CVE Naming Authority (CNA) source for its products and services (see Red Hat classifications).
The following CVSS metrics and score provided are preliminary and subject to review.
CVSS v3 Score Breakdown
| Red Hat | NVD | cve.org | |
|---|---|---|---|
| Base Score | 6.5 | N/A | 6.5 |
| Attack Vector | Network | N/A | Network |
| Attack Complexity | Low | N/A | Low |
| Privileges Required | Low | N/A | Low |
| User Interaction | None | N/A | None |
| Scope | Unchanged | N/A | Unchanged |
| Confidentiality | High | N/A | High |
| Integrity Impact | None | N/A | None |
| Availability Impact | None | N/A | None |
Vector
Red Hat: CVSS:3.1/AV:N/AC:L/PR:L/UI:N/S:U/C:H/I:N/A:N
cve.org: CVSS:3.1/AV:N/AC:L/PR:L/UI:N/S:U/C:H/I:N/A:N
Understanding the Weakness (CWE)
Confidentiality
Technical Impact: Read Memory
An attacker could get secret values such as cryptographic keys, PII, memory addresses, or other information that could be used in additional attacks.
Confidentiality
Technical Impact: Bypass Protection Mechanism
Out-of-bounds memory could contain memory addresses or other information that can be used to bypass ASLR and other protection mechanisms in order to improve the reliability of exploiting a separate weakness for code execution.
Availability
Technical Impact: DoS: Crash, Exit, or Restart
An attacker could cause a segmentation fault or crash by causing memory to be read outside of the bounds of the buffer. This is especially likely when the code reads a variable amount of data and assumes that a sentinel exists to stop the read operation, such as a NUL in a string.
Other
Technical Impact: Varies by Context
The read operation could produce other undefined or unexpected results.
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