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rsync CVE-2026-70457

| EUVDEUVD-2026-58047 HIGH
Incorrect Calculation of Buffer Size (CWE-131)
2026-08-13 VulnCheck
8.3
CVSS 4.0 · Vendor: VulnCheck
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Severity by source

Vendor (VulnCheck) PRIMARY
8.3 HIGH
CVSS:4.0/AV:N/AC:H/AT:N/PR:N/UI:N/VC:N/VI:L/VA:H/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
vuln.today AI
6.5 MEDIUM

Network-reachable via rsync daemon (AV:N), but snprintf truncation requires a precisely crafted size value (AC:H); no auth needed (PR:N); availability impact is high from .bss corruption crash, integrity low from adjacent memory corruption, no confidentiality impact.

3.1 AV:N/AC:H/PR:N/UI:N/S:U/C:N/I:L/A:H
4.0 AV:N/AC:H/AT:N/PR:N/UI:N/VC:N/VI:L/VA:H/SC:N/SI:N/SA:N
SUSE
6.5 MEDIUM
AV:N/AC:H/PR:N/UI:N/S:U/C:N/I:L/A:H
Red Hat
6.5 MEDIUM
qualitative

Primary rating from Vendor (VulnCheck).

CVSS VectorVendor: VulnCheck

Attack Vector
Network
Attack Complexity
High
Privileges Required
None
User Interaction
None
Scope
X

Lifecycle Timeline

3
Source Code Evidence Fetched
Aug 13, 2026 - 15:43 vuln.today
Analysis Generated
Aug 13, 2026 - 15:43 vuln.today
CVE Published
Aug 13, 2026 - 14:44 cve.org
HIGH 8.3

DescriptionCVE.org

rsync 3.2.3 before 3.5.0 contains an out-of-bounds write in parse_size_arg() where the return value of snprintf() is used directly as an index into a .bss-segment array without bounds checking. When snprintf truncates the formatted size string, the return value equals the number of characters that would have been written including the truncated portion, and this value may exceed the array length. The subsequent indexed write targets memory outside the intended array bounds, corrupting .bss memory.

AnalysisAI

Out-of-bounds write in rsync 3.2.3 through 3.4.x corrupts .bss-segment memory via misuse of snprintf() return semantics in parse_size_arg(), enabling remote denial-of-service and potential memory corruption with high availability impact. The CVSS 4.0 score of 8.3 with AV:N/PR:N reflects that an unauthenticated remote attacker can reach the vulnerable code path, though AC:H indicates the truncation condition requires a specifically crafted size argument. No public exploit code or active exploitation (CISA KEV) has been identified at time of analysis. The fix is confirmed in v3.5.0, designated a major security release by the maintainers.

Technical ContextAI

rsync is a ubiquitous file-synchronization utility widely used for backups, deployments, and mirroring across Linux, macOS, and UNIX systems. The vulnerability resides in parse_size_arg(), the function responsible for parsing human-readable size arguments (e.g., --max-size, --min-size, block-size specifications). The flaw stems from misinterpreting snprintf() semantics: snprintf() returns the number of characters that *would have been written* if the buffer were large enough, not the number actually written. When formatting a size string that exceeds the destination buffer, snprintf() truncates the output but returns the full intended length. This return value is then used directly as an array index into a statically allocated .bss-segment array without bounds validation. Since the .bss segment holds global and static variables, an out-of-bounds write at that index corrupts adjacent program state. CWE-131 (Incorrect Calculation of Buffer Size) describes the root cause: the developer incorrectly treats the snprintf return value as a valid in-bounds index. Affected product scope per CPE is cpe:2.3:a:rsyncproject:rsync:*:*:*:*:*:*:*:* covering versions 3.2.3 up to (but not including) 3.5.0.

RemediationAI

Upgrade to rsync 3.5.0 immediately. The maintainers designated v3.5.0 a major security release; the release is confirmed via the tagged GitHub release at https://github.com/RsyncProject/rsync/releases/tag/v3.5.0 and corresponds to the changelog at https://download.samba.org/pub/rsync/NEWS#3.5.0. For environments where upgrading is not immediately feasible, restrict rsync daemon exposure by binding the rsyncd service to loopback or internal interfaces only, thereby removing the AV:N attack surface. Blocking inbound rsync connections (default TCP 873) at the perimeter firewall prevents unauthenticated remote exploitation but does not protect against locally-initiated rsync operations. If rsync is invoked as a client connecting to external servers, note that a malicious or compromised server could also supply crafted responses; in this case, allowlisting trusted server addresses reduces risk. These compensating controls do not eliminate the vulnerability and should be treated as temporary measures pending the upgrade to 3.5.0.

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Vendor StatusVendor

SUSE

Severity: Moderate
Product Status
SUSE Linux Enterprise High Performance Computing 15 SP4-ESPOS Affected
SUSE Linux Enterprise High Performance Computing 15 SP4-LTSS Affected
SUSE Linux Enterprise High Performance Computing 15 SP5-ESPOS Affected
SUSE Linux Enterprise High Performance Computing 15 SP5-LTSS Affected
SUSE Linux Enterprise Micro 5.3 Affected

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CVE-2026-70457 vulnerability details – vuln.today

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