CVE-2026-53791: rsyncproject rsync Authentication Bypass by Spoofing
Vulnerability summary
CVE-2026-53791 is a critical (CVSS 9.1) Authentication Bypass by Spoofing vulnerability in rsyncproject rsync. EPSS estimates a 0.50% chance of exploitation in the next 30 days, higher than 41.6% of scored vulnerabilities.
Advisory lineage
Upstream 0 · Downstream 11 · Related 8Timeline
- 13-08-2026PublishedVulnerability first disclosed.
- 14-08-2026Last modifiedVulnerability information updated.
Description
rsync daemon before 3.5.0 contains an IP address spoofing vulnerability that allows unauthenticated remote attackers to bypass IP-based access controls by sending a crafted PROXY protocol header with a forged source address. Attackers who can connect directly to the rsync daemon can inject a spoofed source IP in the PROXY protocol header to circumvent hosts allow/deny rules, gaining unauthorized access that would otherwise be blocked based on their real source address.
CVSS metrics
8 scores · 5 sources · 2 versions- OSV · AlpineEcosystem advisory · calculated9.1CriticalCVSS:4.0/AV:N/AC:L/AT:P/PR:N/UI:N/VC:H/VI:H/VA:N/SC:N/SI:N/SA:N/E:X/CR:X/IR:X/AR:X/MAV:X/MAC:X/MAT:X/MPR:X/MUI:X/MVC:X/MVI:X/MVA:X/MSC:X/MSI:X/MSA:X/S:X/AU:X/R:X/V:X/RE:X/U:X
- OSV · UbuntuEcosystem advisory · calculated9.1CriticalCVSS:4.0/AV:N/AC:L/AT:P/PR:N/UI:N/VC:H/VI:H/VA:N/SC:N/SI:N/SA:N
- OSV · DebianEcosystem advisory · calculated9.1CriticalCVSS:4.0/AV:N/AC:L/AT:P/PR:N/UI:N/VC:H/VI:H/VA:N/SC:N/SI:N/SA:N/E:X/CR:X/IR:X/AR:X/MAV:X/MAC:X/MAT:X/MPR:X/MUI:X/MVC:X/MVI:X/MVA:X/MSC:X/MSI:X/MSA:X/S:X/AU:X/R:X/V:X/RE:X/U:X
- NVDNIST9.1CriticalCVSS:4.0/AV:N/AC:L/AT:P/PR:N/UI:N/VC:H/VI:H/VA:N/SC:N/SI:N/SA:N/E:X/CR:X/IR:X/AR:X/MAV:X/MAC:X/MAT:X/MPR:X/MUI:X/MVC:X/MVI:X/MVA:X/MSC:X/MSI:X/MSA:X/S:X/AU:X/R:X/V:X/RE:X/U:X
- OSV · UbuntuEcosystem advisory · calculated9.1CriticalCVSS:3.1/AV:N/AC:L/PR:N/UI:N/S:U/C:H/I:H/A:N
- NVDNIST9.1CriticalCVSS:3.1/AV:N/AC:L/PR:N/UI:N/S:U/C:H/I:H/A:N
EPSS trend
Probability
0.50%
Chance of exploitation in the next 30 days
Percentile
42%
Versus all other CVEs
30-day change
0.00 pp
From 0.50% on 20-09-2026
Known exploited
Compare KEV catalogsNot in any of the 3 tracked catalogs.
Public exploits
0 foundNo public exploits indexed.
Weaknesses
CWE · root causeAffected systems
Alpine1 product
- rsync< 3.5.0-r0
Debian1 product
- rsyncAll versions (No fix recorded) | < 3.5.0+ds1-0+deb13u1 | < 3.5.0+ds1-1
Rsyncproject1 product
- rsync≤ 3.4.4
Samba1 product
- rsync< 3.5.0
Ubuntu1 product
- rsyncAll versions (No fix recorded)
5 vendors · 5 products
References
9 links- www.vulncheck.com/advisories/rsync-daemon-ip-spoofing-via-proxy-protocol-headerThird Party AdvisoryRelease Notes
