Security Bulletin: Multiple Vulnerabilities in the Linux kernel affect the IBM FlashSystem models 840 and 900

Summary

There are vulnerabilities in the Linux kernel to which the IBM FlashSystem™ 840 and FlashSystem 900 are susceptible (CVE-2019-11477, CVE-2019-11478, and CVE-2019-11479). An exploit of these vulnerabilities could allow a remote attacker to cause a denial of service condition.

Vulnerability Details

CVEID:CVE-2019-11479
**DESCRIPTION:**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, and is fixed in commits 967c05aee439e6e5d7d805e195b3a20ef5c433d6 and 5f3e2bf008c2221478101ee72f5cb4654b9fc363.
CVSS Base score: 7.5
CVSS Temporal Score: See: https://exchange.xforce.ibmcloud.com/vulnerabilities/162665 for the current score.
CVSS Vector: (CVSS:3.0/AV:N/AC:L/PR:N/UI:N/S:U/C:N/I:N/A:H)

CVEID:CVE-2019-11477
**DESCRIPTION:**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, and is fixed in commit 3b4929f65b0d8249f19a50245cd88ed1a2f78cff.
CVSS Base score: 7.5
CVSS Temporal Score: See: https://exchange.xforce.ibmcloud.com/vulnerabilities/162662 for the current score.
CVSS Vector: (CVSS:3.0/AV:N/AC:L/PR:N/UI:N/S:U/C:N/I:N/A:H)

CVEID:CVE-2019-11478
**DESCRIPTION:**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, and is fixed in commit f070ef2ac66716357066b683fb0baf55f8191a2e.
CVSS Base score: 7.5
CVSS Temporal Score: See: https://exchange.xforce.ibmcloud.com/vulnerabilities/162664 for the current score.
CVSS Vector: (CVSS:3.0/AV:N/AC:L/PR:N/UI:N/S:U/C:N/I:N/A:H)

Affected Products and Versions

Storage Node machine type and models (MTMs) affected:

• 9846-AE1 and 9848-AE1
• 9846-AE2 and 9848-AE2
• 9846-AE3 and 9848-AE3

Supported storage node code versions which are affected

• VRMFs prior to 1.5.2.6
• VRMFs prior to 1.6.1.1

Remediation/Fixes

9840-AE1 and 9843-AE1

FlashSystem 900 MTMs:

9843-UF3, 9840-AE2, 9843-AE2, 9840-AE3, and 9843-AE3

|

Code fixes are now available, the minimum VRMF containing the fix depending on the code stream:

Fixed Code VRMF:

1.6 stream: 1.6.1.1

1.5 stream: 1.5.2.6

| N/A | FlashSystem 840 and FlashSystem 900 fixes are available at IBM’s Fix Central website.

Workarounds and Mitigations

Upgrade to a remediated code level.