CISA Warning on RESURGE Malware Exploiting Ivanti Connect Secure Zero-Day
CISA published updated technical details and warnings about RESURGE, a stealthy Linux implant used in zero-day intrusions against Ivanti Connect Secure appliances. The activity is tied to exploitation of CVE-2025-0282 (a stack-based buffer overflow) affecting Ivanti Connect Secure as well as related Policy Secure and ZTA Gateway products; exploitation was observed beginning in December 2024, and CISA later added the CVE to its Known Exploited Vulnerabilities (KEV) catalog. CISA’s analysis was based on artifacts recovered from a compromised Ivanti device at a critical infrastructure organization, indicating the malware is being used in real-world intrusions rather than as a proof-of-concept.
RESURGE is identified as a Linux shared object, libdsupgrade.so, designed for persistence and stealth, including rootkit/bootkit-like behavior and the ability to remain dormant by passively waiting for specific inbound TLS connections instead of beaconing. The implant reportedly hooks accept() to inspect inbound TLS traffic and uses a CRC32-based TLS fingerprint scheme to identify “legitimate” operator connections; reporting also notes use of a fake Ivanti certificate as an authentication artifact that can serve as a detection signature, followed by a mutually authenticated TLS session. The intrusion set also deployed a SPAWNSLOTH variant (liblogblock.so) for log tampering and a custom tool (dsmain) used to manipulate coreboot images/firmware and filesystem contents for persistence; reporting attributes the broader campaign to China-linked UNC5221 and urges defenders to apply Ivanti fixes and hunt using CISA’s updated IOCs to identify and eradicate latent infections.
Timeline
Mar 2, 2026
CISA publishes updated technical details on RESURGE malware
CISA released updated technical details describing RESURGE as a Linux shared-object implant with passive command-and-control, rootkit and bootkit capabilities, and persistence through coreboot image modification. The agency also urged administrators to use updated indicators of compromise, reset credentials, and rebuild affected devices from factory reset or verified clean images.
Jan 8, 2025
CISA adds CVE-2025-0282 to Known Exploited Vulnerabilities catalog
CISA added CVE-2025-0282 to its Known Exploited Vulnerabilities Catalog after confirming in-the-wild exploitation. The listing formally recognized the Ivanti Connect Secure flaw as actively exploited.
Dec 15, 2024
UNC5221 begins zero-day exploitation of CVE-2025-0282
Researchers assessed that the China-nexus threat actor UNC5221 began exploiting Ivanti Connect Secure vulnerability CVE-2025-0282 as a zero-day in mid-December 2024. The activity targeted Ivanti Connect Secure devices and led to intrusions at victim organizations, including critical infrastructure.
Dec 1, 2024
CISA observes active exploitation of Ivanti Connect Secure devices
CISA reported that active exploitation of CVE-2025-0282 against Ivanti Connect Secure devices was underway beginning in December 2024. Analysis of a compromised critical infrastructure organization uncovered the RESURGE malware along with SPAWNSLOTH log-tampering and the dsmain binary used for persistence.
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