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Attackers targeted multiple Juniper Networks Junos OS flaws affecting SRX and EX devices, focusing on the J-Web interface and chaining vulnerabilities including CVE-2023-36845, CVE-2023-36846, CVE-2023-36847, and CVE-2023-36851 to achieve unauthenticated remote code execution. Security monitoring observed exploitation activity beginning on 2023-09-13 after the vulnerabilities were disclosed, with the issue affecting internet-exposed network infrastructure.
One observed exploit attempt specifically targeted CVE-2023-36845 and used a crafted POST request with PHPRC and auto_prepend_file parameters to try to access /etc/passwd, indicating active probing for code execution and file disclosure on vulnerable systems. Most detected source traffic was attributed to Malaysia, with a smaller share linked to the United States, and defenders were urged to update affected Junos OS versions immediately to reduce exposure.
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MBSD-SOC reported detecting attack activity targeting the Juniper Junos OS vulnerabilities beginning on 2023-09-13. The attacks targeted affected SRX and EX devices, particularly via the J-Web interface.
Among the detected activity, MBSD-SOC observed an exploit attempt for CVE-2023-36845 that tried to access /etc/passwd. The payload used a crafted POST request with PHPRC=/dev/fd/0 and auto_prepend_file set to /etc/passwd.
The MBSD report states that CVE-2023-36851 was additionally published in September 2023 as part of the Junos OS vulnerability set being exploited. It was referenced alongside CVE-2023-36844, CVE-2023-36845, CVE-2023-36846, and CVE-2023-36847.
In August 2023, multiple Juniper Networks Junos OS vulnerabilities affecting SRX and EX series devices were publicly disclosed in an out-of-cycle security bulletin. The flaws could be chained through the J-Web interface to enable unauthenticated remote code execution.
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Juniper Networks disclosed multiple high-severity vulnerabilities in **Junos OS** and **SRX/MX** platforms, including remotely exploitable denial-of-service flaws and local privilege-escalation issues. The most exposed bugs include **`CVE-2026-33790`**, which lets an unauthenticated attacker crash the `srxpfe` packet forwarding engine on **SRX Series** firewalls by sending a malformed **ICMPv6** packet to devices with **NAT64** enabled, and **`CVE-2026-33778`**, which allows a malformed initial **ISAKMP** packet to crash the `kmd` or `iked` daemons on **SRX** and **MX** systems providing IPsec VPN services. Juniper said repeated exploitation can sustain outages by forcing affected processes into crash loops, and that fixes were released through security bulletins including **`JSA107874`** and **`JSA107868`**. Juniper also fixed **`CVE-2026-33785`**, a missing authorization flaw in **MX Series** routers that allows any locally authenticated user to run privileged `request csds` commands and potentially compromise managed infrastructure in **JDM/CSDS** deployments, and **`CVE-2026-21916`**, a symlink-handling bug in the Junos CLI that can let a low-privileged user gain **root** when another user performs a configuration commit. Affected versions span several supported Junos release trains, with fixes issued on April 8, 2026; some older branches, including certain end-of-life releases, do not have patches. Detection guidance from Juniper and Tenable relies largely on version auditing, configuration review for exposed features such as NAT64 and IPsec, and monitoring for daemon crashes, suspicious `file link` activity, unexpected root access, and abuse of privileged management commands.
Jun 29, 2026
Juniper disclosed **CVE-2026-21902**, a critical **remote code execution** vulnerability in *Junos OS Evolved* affecting **PTX Series** routers. The issue is an **incorrect permission assignment for a critical resource** in the **On-Box Anomaly Detection** framework; if the service is reachable over the network, an **unauthenticated attacker** can execute code as **root**, enabling full device takeover. The service is described as running as root and being enabled by default, increasing impact where exposure exists. watchTowr researchers reported the flaw and published technical analysis indicating the affected framework is intended for internal process communication and “should only be reachable” via internal interfaces, but may become accessible depending on configuration. Juniper advised customers to **restrict/filter access** (e.g., via **firewall rules or ACLs**) and indicated a patch would follow; impacted releases called out include **25.4R1-S1-EVO** and **25.4R2-EVO**, while **non-Evolved Junos OS** releases prior to `25.4R1-EVO` were reported as not impacted. Juniper stated it had **no evidence of active exploitation** at the time of disclosure.
Jun 29, 2026
Juniper disclosed a **critical remote code execution** vulnerability in **Junos OS Evolved** running on **PTX Series** routers that can allow an **unauthenticated, network-based attacker** to execute code as **root** and potentially take full control of affected devices (**CVE-2026-21902**). The flaw stems from **incorrect permission assignment** in the *On-Box Anomaly Detection* framework, which is intended to be reachable only by internal processes over an internal routing instance but is exposed via an externally reachable port; the vulnerable service runs as **root** and is **enabled by default**. Affected versions are **25.4** releases prior to **`25.4R1-S1-EVO`** and **`25.4R2-EVO`** on PTX Series; **standard (non-Evolved) Junos OS** and Junos OS Evolved versions before **`25.4R1-EVO`** are not impacted. Juniper released fixes in **`25.4R1-S1-EVO`**, **`25.4R2-EVO`**, and **`26.2R1-EVO`**, and at the time of advisory publication stated it was **not aware of active exploitation**; guidance includes prioritizing patching and, where immediate updates are not possible, restricting access to the exposed endpoints using **firewall filters/ACLs**. The Canadian Centre for Cyber Security echoed the vendor advisory and urged administrators to apply the updates.
Jun 29, 2026