Description
The fanx_fingerprint function in ssl/sslxprint.c of ssldump allocates a heap buffer for formatting FAN/1 X.509 certificate fingerprints. The allocation size is computed as strlen(b64) + strlen(hex) + 31, but the format string "fan1:x509:server:passive:%s:sha256:%s" contains 33 fixed characters in addition to the two variable-length fields and a null terminator, requiring strlen(b64) + strlen(hex) + 34 bytes. This miscalculation results in a 3-byte heap-based buffer overflow on every invocation of the function with valid inputs. The overflow occurs because sprintf writes the full formatted string into the undersized heap buffer without bounds checking. An attacker who can supply a crafted pcap file containing a TLS X.509 certificate to a user running ssldump with FAN/1 fingerprinting enabled (for example with the -j -N options) can trigger the overflow. The resulting heap corruption may lead to denial of service through a crash or, in a worst-case scenario, arbitrary code execution in the context of the user running ssldump. The vulnerability is deterministic and requires no special privileges beyond the ability to provide input to the tool.
Published: 2026-10-16
Score: 6.8 Medium
EPSS: < 1% Very Low
KEV: No
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Remediation

Vendor Solution

The fix replaces the hardcoded size calculation and unbounded sprintf with a two-step snprintf approach: first computing the exact required output length via snprintf(NULL, 0, format, b64, hex), then allocating precisely that length plus one byte for the null terminator via calloc, and finally writing the formatted string with a bounded snprintf. This eliminates the undersized allocation and guarantees the write never exceeds the allocated buffer.

Tracking

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History

Fri, 16 Oct 2026 13:30:00 +0000

Type Values Removed Values Added
Metrics ssvc

{'options': {'Automatable': 'no', 'Exploitation': 'none', 'Technical Impact': 'partial'}, 'version': '2.0.3'}


Fri, 16 Oct 2026 05:45:00 +0000

Type Values Removed Values Added
Description The fanx_fingerprint function in ssl/sslxprint.c of ssldump allocates a heap buffer for formatting FAN/1 X.509 certificate fingerprints. The allocation size is computed as strlen(b64) + strlen(hex) + 31, but the format string "fan1:x509:server:passive:%s:sha256:%s" contains 33 fixed characters in addition to the two variable-length fields and a null terminator, requiring strlen(b64) + strlen(hex) + 34 bytes. This miscalculation results in a 3-byte heap-based buffer overflow on every invocation of the function with valid inputs. The overflow occurs because sprintf writes the full formatted string into the undersized heap buffer without bounds checking. An attacker who can supply a crafted pcap file containing a TLS X.509 certificate to a user running ssldump with FAN/1 fingerprinting enabled (for example with the -j -N options) can trigger the overflow. The resulting heap corruption may lead to denial of service through a crash or, in a worst-case scenario, arbitrary code execution in the context of the user running ssldump. The vulnerability is deterministic and requires no special privileges beyond the ability to provide input to the tool.
Title ssldump Heap Buffer Overflow in FAN/1 X.509 Fingerprint Formatting
First Time appeared Adulau
Adulau ssldump
Weaknesses CWE-122
CWE-787
CPEs cpe:2.3:a:adulau:ssldump:*:*:*:*:*:*:*:*
Vendors & Products Adulau
Adulau ssldump
References
Metrics cvssV4_0

{'score': 6.8, 'vector': 'CVSS:4.0/AV:L/AC:L/AT:N/PR:N/UI:A/VC:N/VI:H/VA:H/SC:N/SI:N/SA:N'}


cve-icon MITRE

Status: PUBLISHED

Assigner: CIRCL

Published:

Updated: 2026-10-16T12:30:53.251Z

Reserved: 2026-10-16T05:24:32.520Z

Link: CVE-2026-111458

cve-icon Vulnrichment

Updated: 2026-10-16T12:30:48.643Z

cve-icon NVD

Status : Deferred

Published: 2026-10-16T06:17:09.510

Modified: 2026-10-16T20:04:29.760

Link: CVE-2026-111458

cve-icon Redhat

No data.

cve-icon OpenCVE Enrichment

Updated: 2026-10-16T15:15:14Z

Weaknesses