CVE-2026-90141 in Linux
Summary
by MITRE • 09/17/2026
In the Linux kernel, the following vulnerability has been resolved:
ipvs: fix integer overflow in ftp helper port/address parsing
ip_vs_ftp_get_addrport() accumulates decimal digits into a __u16 (hport) and into unsigned char (p[]) without checking for overflow.
A crafted FTP PASV/EPSV response with an over-long port or address octet wraps the value, so the helper configures the data connection with a truncated port/address.
The netfilter conntrack FTP helper had the same defect, fixed in commit 2b413fc689ba ("netfilter: nf_conntrack_ftp: avoid u16 overflows"). Apply the equivalent fix here: widen the port accumulator to u32 and reject values above 65535, and reject address octets above 255.
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Analysis
by VulDB Data Team • 09/17/2026
The Linux kernel's IP Virtual Server (IPVS) subsystem contains a critical integer overflow vulnerability within its FTP helper module, specifically in the ip_vs_ftp_get_addrport function. This component is responsible for parsing incoming FTP PASV and EPSV responses to identify the correct port and address for establishing data connections. The flaw arises because the implementation accumulates decimal digits into a sixteen-bit unsigned integer variable named hport without performing any bounds checking during the accumulation process. Similarly, individual octets of the IP address are stored in an array of eight-bit unsigned characters without validation against maximum allowable values. This lack of input sanitization allows crafted FTP responses containing excessively long port numbers or invalid address components to bypass standard parsing logic and trigger arithmetic wrapping behavior inherent to fixed-width integer types.
When a maliciously constructed FTP server responds with a PASV or EPSV command that includes an over-long port number, the accumulation operation causes the value to wrap around due to exceeding the maximum capacity of the sixteen-bit unsigned integer type. This results in a truncated and incorrect port number being passed to subsequent connection establishment routines. In cases where address octets exceed their valid range of zero to two hundred fifty-five, similar truncation or wrapping occurs within the eight-bit storage containers. These errors lead to the IPVS load balancer configuring data connections with fundamentally wrong network parameters. Instead of connecting to the intended service endpoint on a legitimate port and address, the system attempts to route traffic to an unintended destination based on the wrapped values.
The operational impact of this vulnerability is significant for environments relying on IPVS for high availability or load balancing of FTP services. Attackers can exploit this flaw by hosting a malicious FTP server that sends specially crafted PASV or EPSV responses containing oversized numeric fields. Upon receiving such a response, the kernel's netfilter subsystem processes it through the vulnerable helper function, resulting in misconfigured connection tracking entries and data channel setups. This can lead to denial of service conditions where legitimate users are unable to establish successful file transfers because connections fail due to invalid target addresses or ports. Furthermore, depending on how downstream applications handle these malformed parameters, there may be potential for further exploitation vectors involving unexpected behavior in network stack processing or application-level logic that assumes valid input from the kernel helper modules.
This issue mirrors a previously identified defect found in the netfilter conntrack FTP helper module, which was addressed through commit 2b413fc689ba to prevent similar sixteen-bit overflow scenarios. The current fix applies equivalent remediation measures directly within the IPVS context by widening the port accumulator variable from a sixteen-bit unsigned integer to a thirty-two-bit unsigned integer type. This change ensures that intermediate calculations can accommodate larger values without immediate wrapping, allowing for proper validation before final assignment. Additionally, explicit checks are now enforced to reject any accumulated port value exceeding sixty-five thousand five hundred thirty-five and address octets greater than two hundred fifty-five. These constraints align with standard networking protocols where ports must remain within the valid range of zero to sixty-five thousand five hundred thirty-five and IPv4 addresses consist of four octets each ranging from zero to two hundred fifty-five.
From a classification perspective, this vulnerability corresponds to CWE-190 Integer Overflow or Wraparound, as it involves arithmetic operations exceeding the capacity of the allocated data type leading to unintended results. It also relates to CWE-20 Improper Input Validation since the root cause is the failure to verify that parsed numeric values fall within expected bounds before use in critical network configuration tasks. In terms of attack patterns, this flaw could be leveraged by adversaries aiming for Denial of Service against load-balanced FTP infrastructure or potentially as part of a broader campaign involving traffic redirection if combined with other vulnerabilities affecting routing decisions. Mitigation requires applying the kernel patch that implements these validation checks and widening data types to prevent overflow conditions during FTP protocol parsing operations within IPVS environments.