Denial of Service Problems with Linksys Products

Through the iDEFENSE vulnerability contributor program, Alex S. Harasic disclosed information on denial of service problem in several Linksys products. The products include:

  • BEFW11S4, Wireless Access Point Router with 4-Port Switch – Version 2
  • BEFSR11, EtherFast Cable/DSL Router
  • BEFSR41, EtherFast Cable/DSL Router with 4-Port Switch
  • BEFSRU31, EtherFast Cable/DSL Router with USB and 3-Port Switch

The BEFW11S4, BEFSR11, BEFSR41 and BEFSRU31 units can be crashed when several thousand characters are passed in the password field of the device’s web management interface. Exploitation simply requires the use of a web browser that can send long Basic Authentication fields to the affected router’s interface.

Linksys released firmware update (1.43.3) which can be downloaded from

In a related post to the BugTraq mailing list, Seth Bromberger noted that Linksys confirmed that the same problem also affects BEFVP41, BEFSX41, BEFSR81, BEFN2PS4 and HPRO200. Vulnerable versions for this additional products include releases later than 1.42.7 (2.42.7 for the BEFSR81 unit).

Linksys support added: “Until the updated firmware is released, we recommend that users downgrade the firmware to an earlier release, or minimize the risk of an attack by disabling remote management of the device.”


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