CVE-2025-4877 | Libssh: write beyond bounds in binary to base64 conversion functions

There's a vulnerability in the libssh package where when a libssh consumer passes in an unexpectedly large input buffer to ssh_get_fingerprint_hash() function. In such cases the bin_to_base64() function can experience an integer overflow leading to a memory under allocation, when that happens it's possible that the program perform out of bounds write leading to a heap corruption. This issue affects only 32-bits builds of libssh.

Published: 2025-08-20 Last update: 2026-05-19 Assigner: [email protected] Source: [email protected]
NVD Status：Deferred，CVE State: published
View at NVD, CVE.org, EUVD

CVE-2025-4877 is rated Low Risk (18.4/100): CVSS Medium severity, with low exploitation likelihood (EPSS 0.01%). Low composite risk—no urgent action required; patch on your normal maintenance cycle and revisit priority if CVSS or EPSS increases.

Risk is dynamic; we continuously reassess and refresh what is shown on this page as upstream context changes.

Exploit prediction scoring system (EPSS) score for CVE-2025-4877

EPSS lead: Daily EPSS estimates relative likelihood of exploitation; percentile ranks this CVE among scored vulnerabilities (higher = more severe relative rank).

# Date Old EPSS score New EPSS score Delta (New - Old)
1 2025-08-21 — 0.01% —

Full EPSS history (1 record total)

Common vulnerability scoring system (CVSS) metrics for CVE-2025-4877

CVSS metrics for this CVE.

Base score Version Severity Vector Exploitability Impact Score source
4.5 3.1 MEDIUM
CVSS:3.1/AV:L/AC:H/PR:L/UI:N/S:U/C:L/I:L/A:L Click to expand
Attack vector (AV:L)
They already need access on the box, or another person has to do something wrong; it’s not a remote drive-by.
Attack complexity (AC:H)
Even with access, the exploit needs extra luck, timing, or a fussy environment to actually work.
Privileges required (PR:L)
A normal user session is enough; they don’t have to be admin.
User interaction (UI:N)
Nobody has to click “OK” or open a trap file; it can work without a victim helping.
Scope (S:U)
Damage stays in the same “trust bubble” as the broken component—no big spill into unrelated systems.
Confidentiality (C:L)
Some sensitive info could get out, but not a total data dump.
Integrity (I:L)
Attackers could change some data, but it’s limited—not everything goes.
Availability (A:L)
Might cause slowdowns, glitches, or partial disruption—not a full brick.
 1.0 3.4 [email protected]

Weakness enumeration for CVE-2025-4877

GitHub Security Advisory for CVE-2025-4877

GHSA-pwrf-jm93-99r3 · Severity: medium — There's a vulnerability in the libssh package where when a libssh consumer passes in an...

OS Trackers for CVE-2025-4877

vendor priority summary link
alpine medium CVE-2025-4877: 1 source package rows (libssh); 2 state rows across 2 repos (3.22-community, edge-community); fixed 2, open 0. https://security.alpinelinux.org/vuln/CVE-2025-4877
debian not yet assigned CVE-2025-4877 not yet assigned priority: Debian including 1 source packages (libssh), 5 status rows across 5 suites (bookworm, bullseye, forky, sid, trixie): resolved 5. https://security-tracker.debian.org/tracker/CVE-2025-4877
redhat medium — https://access.redhat.com/security/cve/CVE-2025-4877
suse medium CVE-2025-4877 severity moderate: SUSE including 352 source package names (0.0.17-1.1:libssh-config-0.9.8-150600.11.3.1, 0.0.17-1.1:libssh4-0.9.8-150600.11.3.1, …), 1051 product×package rows across 364 product lines (Container bci/kiwi, Container bci/spack, … (364 product lines)): Fixed 830, Known Affected 221. https://www.suse.com/security/cve/CVE-2025-4877/
ubuntu medium CVE-2025-4877 medium priority: Ubuntu including 1 source packages (libssh), 8 status rows across 8 suites (bionic, focal, jammy, noble, oracular, plucky, upstream, xenial): released 8. https://ubuntu.com/security/CVE-2025-4877

Affected software / configurations for CVE-2025-4877

Vendor Product Version Raw CPE
No affected products in dataset.

References for CVE-2025-4877

cvelogic Threat Intelligence