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AUSCERT External Security Bulletin Redistribution
JSA11159 - 2021-04 Security Bulletin: Junos OS: J-Web has an Improper
Neutralization of CRLF Sequences in its HTTP Headers which allows an
attacker to carry out multiple types of attacks. (CVE-2021-0268)
27 May 2021
AusCERT Security Bulletin Summary
Product: Junos OS
Publisher: Juniper Networks
Operating System: Juniper
Impact/Access: Modify Arbitrary Files -- Remote with User Interaction
Cross-site Scripting -- Remote with User Interaction
Access Confidential Data -- Remote with User Interaction
Reduced Security -- Remote with User Interaction
CVE Names: CVE-2021-0268
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2021-04 Security Bulletin: Junos OS: J-Web has an Improper Neutralization of
CRLF Sequences in its HTTP Headers which allows an attacker to carry out multiple
types of attacks. (CVE-2021-0268)
Article ID : JSA11159
Last Updated: 26 May 2021
Version : 2.0
This issue affects Junos OS 18.1, 18.2, 18.3, 18.4, 19.1, 19.2, 19.3, 19.4,
An Improper Neutralization of CRLF Sequences in HTTP Headers ('HTTP Response
Splitting') weakness in J-web of Juniper Networks Junos OS leads to buffer
overflows, segment faults, or other impacts, which allows an attacker to modify
the integrity of the device and exfiltration information from the device
The weakness can be exploited to facilitate cross-site scripting (XSS), cookie
manipulation (modifying session cookies, stealing cookies) and more. This
weakness can also be exploited by directing a user to a seemingly legitimate link
from the affected site.
The attacker requires no special access or permissions to the device to carry out
This issue affects:
Juniper Networks Junos OS:
o 18.1 versions prior to 18.1R3-S11;
o 18.2 versions prior to 18.2R3-S5;
o 18.3 versions prior to 18.3R2-S4, 18.3R3-S3;
o 18.4 versions prior to 18.4R2-S5, 18.4R3-S3;
o 19.1 versions prior to 19.1R2-S2, 19.1R3-S2;
o 19.2 versions prior to 19.2R1-S5, 19.2R2;
o 19.3 versions prior to 19.3R3;
o 19.4 versions prior to 19.4R1-S3, 19.4R2, 19.4R3;
o 20.1 versions prior to 20.1R1-S2, 20.1R2.
o This issue does not affect Juniper Networks Junos OS versions prior to
The following minimal configuration is necessary:
[system services web-management http]
[system services web-management https]
Juniper SIRT is not aware of any malicious exploitation of this vulnerability.
This issue was found during internal product security testing or research.
This issue has been assigned CVE-2021-0268 .
The following software releases have been updated to resolve this specific
issue: 18.1R3-S11, 18.2R3-S5, 18.3R2-S4, 18.3R3-S3, 18.4R2-S5, 18.4R3-S3,
19.1R2-S2, 19.1R3-S2, 19.2R1-S5, 19.2R2, 19.3R3, 19.4R1-S3, 19.4R2, 19.4R3,
20.1R1-S2, 20.1R2, 20.2R1, and all subsequent releases.
This issue is being tracked as 1503569 .
There are no viable workarounds for this issue other than disabling the J-Web
To reduce the risk of exploitation utilize common security BCPs to limit the
exploitable surface by limiting access to network and device to trusted
systems, administrators, networks and hosts.
Software releases or updates are available for download at https://
2021-04-14: Initial Publication.
CVSS Score: 8.8 (CVSS:3.1/AV:N/AC:L/PR:N/UI:R/S:C/C:H/I:L/A:L)
Severity Level: High
Information for how Juniper Networks uses CVSS can be found at KB 16446 "Common
Vulnerability Scoring System (CVSS) and Juniper's Security Advisories."
The Juniper SIRT wishes to thank Luca Ercoli for responsibly reporting one of
the issues resolved in this update.
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