Junos OS: Use of Externally-Controlled Format String
CVE-2024-39529 is a high-severity use of externally-controlled format string vulnerability in Junos OS from Juniper Networks, with a CVSS 3.1 base score of 7.5 out of 10. It can be exploited remotely over the network by an unauthenticated attacker, without any action from a user. The record lists versions 21.4R3-S6, 22.2R3-S3, 22.3R3-S3 as the first without the flaw, so updating Junos OS to one of those releases or later removes the exposure. There is no confirmed exploitation so far. EPSS estimates a 0.48% chance of exploitation within 30 days, which is low compared with other CVEs.
High severity with no evidence of exploitation so far.
What to do
- Update Junos OS to 21.4R3-S6 or 22.2R3-S3 or 22.3R3-S3 or 22.4R3, whichever matches your release line, or a later version.
- Update Junos to 21.4 or a later version.
- Read the advisory on supportportal.juniper.net for workarounds and exact fixed builds.
- Until you can update, restrict network access to the affected service so it is not reachable from untrusted networks.
Affected products and versions
| Vendor | Product | Affected versions | Fixed in |
|---|---|---|---|
| Juniper Networks | Junos OS | before 21.4R3-S6; 22.2 up to, but not including, 22.2R3-S3; 22.3 up to, but not including, 22.3R3-S3; 22.4 up to, but not including, 22.4R3; 23.2 up to, but not including, 23.2R2; before 21.4r3-s6; 22.2 up to, but not including, 22.2r3-s3; 22.3 up to, but not including, 22.3r3-s3; and 2 more ranges | 21.4R3-S6, 22.2R3-S3, 22.3R3-S3, 22.4R3, 23.2R2, 21.4r3-s6 |
| Juniper Networks | Junos | before 21.4; 21.4; 22.2; 22.3; 22.4; 23.2 | 21.4 |
Version data comes from the organisation that assigned the CVE. Confirm against the vendor advisory before deciding you are unaffected.
How the severity score breaks down
- Attack vector
- NetworkCan be exploited remotely over a network, including the internet.
- Attack complexity
- LowNo special conditions are needed; the attack works reliably.
- Privileges required
- NoneNo account or login is needed.
- User interaction
- NoneNo action by a victim is required.
- Scope
- UnchangedImpact stays within the vulnerable component.
- Confidentiality
- NoneNo data is disclosed.
- Integrity
- NoneNothing can be modified.
- Availability
- HighThe component can be taken down completely.
Vector: CVSS:3.1/AV:N/AC:L/PR:N/UI:N/S:U/C:N/I:N/A:H. Scored by CNA (juniper.net).
| Scoring system | Score | Severity | Scored by |
|---|---|---|---|
| CVSS 4.0 | 8.7 | High | CNA (juniper.net) |
| CVSS 3.1 | 7.5 | High | CNA (juniper.net) |
Official description
A Use of Externally-Controlled Format String vulnerability in the Packet Forwarding Engine (PFE) of Juniper Networks Junos OS on SRX Series allows an unauthenticated, network-based attacker to cause a Denial-of-Service (DoS). If DNS Domain Generation Algorithm (DGA) detection or tunnel detection, and DNS-filtering traceoptions are configured, and specific valid transit DNS traffic is received this causes a PFE crash and restart, leading to a Denial of Service. This issue affects Junos OS: * All versions before 21.4R3-S6, * 22.2 versions before 22.2R3-S3, * 22.3 versions before 22.3R3-S3, * 22.4 versions before 22.4R3, * 23.2 versions before 23.2R2.
Source: the CVE record as published by its numbering authority, via NVD and CVE.org.
The underlying weakness: Use of Externally-Controlled Format String
The product uses a function that accepts a format string as an argument, but the format string originates from an external source.
How developers prevent this class of flaw
- Choose a language that is not subject to this flaw.
- Ensure that all format string functions are passed a static string which cannot be controlled by the user, and that the proper number of arguments are always sent to that function as well. If at all possible, use functions that do not support the %n operator in format strings.
- Run compilers and linkers with high warning levels, since they may detect incorrect usage.
More Use of Externally-Controlled Format String vulnerabilities (CWE-134)
Timeline
- CVE record published.
- CISA published its SSVC assessment (exploitation: none, automatable: yes, technical impact: partial).
- Record last changed materially (score, affected products, status or references).
References
Advisories
Other vulnerabilities in Junos OS
- 7.5 High severity
- 9.8 Critical severity
- 9.8 Critical severity
- 8.8 High severity
- 8.8 High severity
- 7.5 High severity
Recent Use of Externally-Controlled Format String vulnerabilities
- 9.8 Critical severity
- 8.8 High severity
- 9.1 Critical severity
- 7.2 High severity
- 8.8 High severity
- 8.1 High severity
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