CVE-2026-55564: Out-of-bounds Read (CVSS 5.4)

Description

FreeRDP is a free implementation of the Remote Desktop Protocol. Prior to 3.27.0, the glyph_cache_get function in libfreerdp/cache/glyph.c checks whether index is greater than cache->number instead of greater than or equal to it. A malicious RDP server can use GLYPH_FRAGMENT_USE replay in update_process_glyph_fragments to make the default cache receive index 254 when cache->number is 254, reading one pointer beyond the entries array and dereferencing it as a glyph. This can crash the client and may disclose adjacent heap data. This issue is fixed in version 3.27.0.

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CVSS v3.1 Score

5.4

MEDIUM

CVSS:3.1/AV:N/AC:L/PR:N/UI:R/S:U/C:L/I:N/A:L

EPSS — Exploit Prediction

0.0033

Probability of exploitation

0.27%

Percentile rank

EPSS estimates the probability that this vulnerability will be exploited in the wild within the next 30 days. A higher score means more likely to be exploited.

Weakness Type (CWE)

CWE-125 Out-of-bounds Read

CWE-193 CWE-193

References

Other References

https://github.com/FreeRDP/FreeRDP/commit/c29324750e3cbcba8761f147b7a5235cc686930f https://github.com/FreeRDP/FreeRDP/pull/12885 https://github.com/FreeRDP/FreeRDP/releases/tag/3.27.0 https://github.com/FreeRDP/FreeRDP/security/advisories/GHSA-6xmj-pr98-cx4c https://github.com/FreeRDP/FreeRDP/security/advisories/GHSA-6xmj-pr98-cx4c

Frequently Asked Questions

What is CVE-2026-55564? +

FreeRDP is a free implementation of the Remote Desktop Protocol. Prior to 3.27.0, the glyph_cache_get function in libfreerdp/cache/glyph.c checks whether index is greater than cache->number instead of greater than or equal to it. A malicious RDP server can use GLYPH_FRAGMENT_USE replay in update_process_glyph_fragments to make the default cache receive index 254 when cache->number is 254, reading one pointer beyond the entries array and dereferencing it as a glyph. This can crash the client and may disclose adjacent heap data. This issue is fixed in version 3.27.0. It has a CVSS v3.1 base score of 5.4 (MEDIUM).

How severe is CVE-2026-55564? +

CVE-2026-55564 has a CVSS v3.1 score of 5.4 out of 10, rated MEDIUM. This is a medium-severity vulnerability that should be remediated as part of regular maintenance. The EPSS score is 0.0033, placing it in the 0th percentile for exploitation probability.

How do I check if I'm vulnerable to CVE-2026-55564? +

You can use Secably's free Website Scanner to check your website for known vulnerabilities. For infrastructure scanning, use the Port Scanner to identify exposed services that may be affected. Check the vendor advisories linked above for specific patch and version information.

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