Medium

SSRF in CPython ftplib.ftpcp() PASV handling

IdentifiersCVE-2026-8328CWE-918· Server-Side Request Forgery (SSRF)

CVE-2026-8328 is a medium-severity vulnerability in CPython's Lib/ftplib.py affecting the ftpcp() function. When CVE-2021-4189 was previously fixed, makepasv() was updated to ignore a server-supplied PASV host address and instead use the actual peer address from getpeername()[0]. However, ftpcp() was not updated accordingly. It still calls parse227() directly and uses the returned, attacker-controllable IP address and port from the FTP server's PASV response, passing them to target.sendport(). As a result, an attacker-controlled FTP server can influence the destination used during FTP copy operations, creating a server-side request forgery condition and enabling FTP bounce-style behavior.

For your environment

Are you exposed to this one?

Mallory correlates every CVE against your assets, your vendors, and active adversary campaigns. Know which vulnerabilities matter for you, not just which ones are loud.

Start free trial

ANALYST BRIEF

Impact, mitigation & remediation

What it means. What to do now. Patch path, mitigations, and the assume-compromise checklist.

Impact

What an attacker gets, and what they’ve been doing with it.

Successful exploitation allows an attacker controlling the FTP server to cause the vulnerable client or intermediary target involved in ftpcp() operations to initiate network connections to an arbitrary IP address and port specified in the malicious PASV response. This can be used for SSRF, unintended internal network access, port interaction/scanning, or FTP bounce-style abuse, depending on network reachability and how ftpcp() is used in the application.

Mitigation

If you can’t patch tonight, do this now.

If an updated CPython release cannot be deployed immediately, avoid using ftplib.ftpcp() with untrusted or attacker-controlled FTP servers. Restrict outbound network access from affected systems to limit arbitrary connection attempts, especially toward internal or sensitive network ranges. Where feasible, disable or replace workflows that rely on ftpcp() until the fix is applied.

Remediation

Patch, then assume compromise.

Apply the vendor-provided patch or upgrade to a CPython release that includes the fix for CVE-2026-8328. The fix should ensure ftpcp() does not trust the server-supplied PASV host address and instead uses the actual peer address consistently, analogous to the earlier makepasv() correction related to CVE-2021-4189.

PUBLIC EXPLOITS

Exploits

No public exploits tracked yet. Mallory keeps watching.

VALID 0 / 0 TOTALView more in app

No public exploit code observed for this vulnerability.

EXPOSURE SURFACE

Affected products & vendors

Products and vendors Mallory has correlated with this vulnerability. Open in Mallory to drill down to specific CPE configurations and version ranges.

VendorProductType

PythonCpythonapplication

PythonPythonapplication

Vendor-confirmed product mapping. Mallory continuously reconciles this list against your asset inventory.

ACTIVITY FEED

Recent activity

7 sources tracked across advisories and community write-ups. News coverage will land here when it surfaces.

7 SOURCESView more in app

No news coverage yet. Advisories and community discussion only.

What this page doesn’t show

The version that knows your environment.

This page is what’s public. Mallory adds the parts that aren’t: which of your assets are affected, which adversaries are exploiting it right now, which detections to deploy, and what to do tonight.

Start free trial

Exposure mapping

Query your assets running an affected version, and investigate the blast radius.

Threat actor evidence

Every observed campaign linking this CVE to a named adversary.

Associated malware

Malware families riding this exploit, with evidence and IOCs.

Detection signatures

YARA, Sigma, Snort, and vendor rules, auto-deployed to your SIEM.

Vendor-by-vendor mapping

Cross-references every affected SKU, including bundled OEM variants.

Social activity6