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Critical Squid Proxy Vulnerability 'Squidbleed' Exposes User Data

Critical Squid Proxy Vulnerability 'Squidbleed' Exposes User Data

First seen 22 Jun 2026, 19:24 UTC • •
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ThreatCluster AI
ThreatCluster •June 23, 2026 at 19:21 UTC
  • •Squidbleed (CVE-2026-47729) is a critical memory leak vulnerability in Squid Proxy.
  • •The flaw has existed since 1997 and can expose sensitive user data in shared environments.
  • •A patch was released in June 2026, and disabling FTP support can help mitigate risks.

A memory leak vulnerability named Squidbleed, tracked as CVE-2026-47729, has been discovered in the Squid web proxy software, affecting versions since 1997. This flaw allows attackers to read beyond memory buffer boundaries in the FTP parser, potentially exposing sensitive data such as authentication credentials and API keys. The vulnerability is particularly dangerous in shared proxy environments, like corporate networks and public Wi-Fi, where multiple users access a single Squid instance. Exploitation requires control over an FTP server accessible from the proxy. A patch was merged into Squid version 8 in April 2026 and released in version 7.6 in June 2026. Disabling FTP support can mitigate risks if FTP is not needed. Researchers from Calif.io discovered the vulnerability with the help of Anthropic's Claude Mythos AI model.

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Updated 106d ago How this analysis works

Timeline

2026-04-01
Patch merged into Squid version 8
A patch addressing the Squidbleed vulnerability was integrated into the upcoming version of Squid.
Feeds.Feedburner
2026-06-01
Squid version 7.6 released
The patched version of Squid, 7.6, was released to address the Squidbleed vulnerability.
Feeds.Feedburner
2026-06-22
Squidbleed vulnerability disclosed
The critical memory leak vulnerability in Squid Proxy was publicly disclosed, affecting user data.
Gbhackers
2026-06-22
Security researchers confirm vulnerability details
Researchers from Calif.io confirmed the existence and implications of the Squidbleed vulnerability.
Cybersecuritynews
2026-06-22
Public exploit for CVE-2026-47729 released
A proof-of-concept exploit appeared on GitHub, lowering the barrier for opportunistic attackers.
GitHub

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