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                         AUSCERT Security Bulletin

                              ASB-2019.0178.2
            Updates for Linux kernel TCP Sad SACK vulnerability
        (CVE-2019-11477, CVE-2019-11478, CVE-2019-11479) (SB10287)
                             9 September 2019

===========================================================================

        AusCERT Security Bulletin Summary
        ---------------------------------

Product:          Multiple McAfee products
Operating System: Linux variants
Impact/Access:    Denial of Service -- Remote/Unauthenticated
Resolution:       Mitigation
CVE Names:        CVE-2019-11479 CVE-2019-11478 CVE-2019-11477
Reference:        ASB-2019.0174
                  ASB-2019.0172
                  ESB-2019.2433
                  ESB-2019.2378

Revision History: September 9 2019: Additional updates provided
                  July      5 2019: Initial Release

OVERVIEW

        Multiple McAfee products are affected by the Linux kernel TCP Sad SACK 
        vulnerability (CVE-2019-11477, CVE-2019-11478, CVE-2019-11479) [1]


IMPACT

        McAfee has provided the following information regarding the vulnerability and impact:
        
        "CVE-2019-11477
        Jonathan Looney discovered that the TCP_SKB_CB(skb)->tcp_gso_segs value was
        subject to an integer overflow in the Linux kernel when handling TCP Selective
        Acknowledgments (SACKs). A remote attacker could use this to cause a denial of
        service. This has been fixed in stable kernel releases 4.4.182, 4.9.182,
        4.14.127, 4.19.52, 5.1.11.
        http://cve.mitre.org/cgi-bin/cvename.cgi?name=CVE-2019-11477
        https://access.redhat.com/security/cve/cve-2019-11477
        
        CVE-2019-11478
        Jonathan Looney discovered that the TCP retransmission queue implementation in
        tcp_fragment in the Linux kernel could be fragmented when handling certain TCP
        Selective Acknowledgment (SACK) sequences. A remote attacker could use this to
        cause a denial of service. This has been fixed in stable kernel releases
        4.4.182, 4.9.182, 4.14.127, 4.19.52, 5.1.11.
        http://cve.mitre.org/cgi-bin/cvename.cgi?name=CVE-2019-11478
        https://access.redhat.com/security/cve/cve-2019-11478
        
        CVE-2019-11479
        Jonathan Looney discovered that the Linux kernel default MSS is hard-coded to
        48 bytes. This allows a remote peer to fragment TCP resend queues significantly
        more than if a larger MSS were enforced. A remote attacker could use this to
        cause a denial of service. This has been fixed in stable kernel releases
        4.4.182, 4.9.182, 4.14.127, 4.19.52, 5.1.11.
        http://cve.mitre.org/cgi-bin/cvename.cgi?name=CVE-2019-11479
        https://access.redhat.com/security/cve/cve-2019-11479
        McAfee Product Vulnerability Status
        The table below shows the status of all currently supported products where
        McAfee provides the operating system. The table is populated with versions and
        dates released as they are made available." [1]


MITIGATION

        McAfee recommends the following actions:
        "Apply workarounds where required and deploy the updates as
        they are made available." [1]
        Further details of vulnerable and fixed software versions and 
        workarounds are provided in the referenced article. [1]


REFERENCES

        [1] McAfee Security Bulletin - Updates for Linux kernel TCP Sad SACK
            vulnerability (CVE-2019-11477, CVE-2019-11478, CVE-2019-11479)
            https://kc.mcafee.com/corporate/index?page=content&id=SB10287

AusCERT has made every effort to ensure that the information contained
in this document is accurate.  However, the decision to use the information
described is the responsibility of each user or organisation. The decision to
follow or act on information or advice contained in this security bulletin is
the responsibility of each user or organisation, and should be considered in
accordance with your organisation's site policies and procedures. AusCERT
takes no responsibility for consequences which may arise from following or
acting on information or advice contained in this security bulletin.

===========================================================================
Australian Computer Emergency Response Team
The University of Queensland
Brisbane
Qld 4072

Internet Email: auscert@auscert.org.au
Facsimile:      (07) 3365 7031
Telephone:      (07) 3365 4417 (International: +61 7 3365 4417)
                AusCERT personnel answer during Queensland business hours 
                which are GMT+10:00 (AEST).
                On call after hours for member emergencies only.
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