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.

The version of freerdp installed on the remote host is prior to 2.11.7-1. It is, therefore, affected by multiple vulnerabilities as referenced in the ALAS2-2026-3840 advisory.

    Heap-buffer-overflow write in TS Gateway RPC fragment receive due to uncapped bind_ack max_xmit_frag

    On TS Gateway connections, rpc->max_recv_frag is initialized to 0x0FF8 (4088) and ReceiveFragment is     allocated to that size. In rpc_bind.c, the client assigns rpc->max_recv_frag =     header.bind_ack.max_xmit_frag from the server without an upper bound. A malicious gateway can set     max_xmit_frag = 0xFFFF while ReceiveFragment is never resized.

    Later, rpc_client.c rejects fragments with if (header.frag_length > rpc->max_recv_frag). When both values     are 65535, the check passes (65535 > 65535 is false). The receive loop then calls rpc_channel_read() -     BIO_read() into the fixed 4088-byte ReceiveFragment, writing up to 65535 bytes and overflowing by up to     61447 attacker-controlled bytes. (CVE-2026-55193)

    Heap-buffer-overflow write in TS Gateway RPC RESPONSE reassembly due to alloc_hint capacity mismatch

    In rpc_client_recv_fragment(), when reassembling a PTYPE_RESPONSE PDU, the client calls     Stream_EnsureCapacity(pdu->s, response->alloc_hint) using only the server-declared alloc_hint.
    Stream_EnsureCapacity() returns success if the existing capacity is already >= alloc_hint, without     considering the current write offset or the actual stub length about to be copied.

    A malicious gateway can set a small alloc_hint (e.g. 100) while sending a large fragment (frag_length =     6000, yielding StubLength [?] 5968). The 4096-byte reassembly buffer is not grown, and     Stream_Write(pdu->s, ..., StubLength) copies attacker-controlled stub data past the end of the heap     allocation. On default builds this may abort via WINPR_ASSERT; on Release builds (NDEBUG) the assert is     elided and the overflow becomes an exploitable heap write.

    This is distinct from the separate ReceiveFragment / bind_ack max_xmit_frag issue (different buffer and     code path in the same gateway module). (CVE-2026-55194)

    Out-of-bounds read in glyph_cache_get via crafted glyph fragments

    A malicious RDP server can trigger an out-of-bounds heap read in a FreeRDP client through the glyph cache.
    glyph_cache_get() bounds-checks the index with > where it should use >= -- the sibling glyph_cache_put()     already gets it right. Since the cache's entries array holds exactly number pointers, an index equal to     number slips past the check and reads one slot past the end, which the caller then dereferences as a     glyph. It's the read-side twin of CVE-2020-11098 (the write side was fixed back in 2.1.2; the read side     never was), and it's still present in 3.25.0 and master. (CVE-2026-55564)

    Integer Overflow in freerdp_image_copy_from_icon_data Bypasses Bounds Check (CVE-2026-55648)

    Out-of-bounds read in the camera device enumerator server (rdpecam) via unterminated DeviceName /     VirtualChannelName (CVE-2026-57157)

    planar_decompress_plane_rle_only: heap OOB read -- incomplete fix for CVE-2026-23530

    The fix for CVE-2026-23530 (GHSA-r4hv-852m-fq7p) correctly adds dimension guardsat the entry point of     freerdp_bitmap_decompress_planar but is incomplete in scope.planar_decompress_plane_rle_only dereferences
    *srcp before validating thatsrcp is within SrcSize. A malicious server can reach this path via a     truncatedRLE planar payload in RDPGFX_CMDID_WIRETOSURFACE_1. (CVE-2026-57158)

Tenable has extracted the preceding description block directly from the tested product security advisory.

Note that Nessus has not tested for these issues but has instead relied only on the application's self-reported version number.

It is, therefore, affected by multiple vulnerabilities as referenced in the ALAS2023-2026-2012 advisory.

    Heap-buffer-overflow write in AVC444 YUV buffer allocation

    In libfreerdp/codec/h264.c, avc444_ensure_buffer() computes the AVC444 YUV444 intermediate buffer size as     piDstSize[x] = piDstStride[x] * padDstHeight using UINT32 arithmetic. When the true product exceeds     UINT32_MAX, the value wraps to a small non-zero integer. The only guard is if (piDstSize[x] == 0) return     FALSE, so non-zero wraps pass. winpr_aligned_recalloc() then allocates a buffer far too small, and     yuv444_context_decode() - YUV420CombineToYUV444() writes using the real stride and rectangle dimensions,     causing a heap-buffer-overflow write.

    The reallocation trigger at lines 498-499 correctly compares against 1ull * piMainStride[0] * padDstHeight     (64-bit), but the allocation at line 504 still uses 32-bit multiply. (CVE-2026-55191)

    Out-of-bounds read in H.264 YUV-to-RGB conversion due to decoder/surface dimension mismatch

    After h264->subsystem->Decompress() returns, all major H.264 backends overwrite h264->pYUVData and     h264->iStride with decoder-internal YUV buffers sized by the H.264 bitstream SPS. These dimensions are     never compared against the RDPGFX surface dimensions stored in h264->width / h264->height.

    areRectsValid() validates region rectangles against the surface width/height passed into     avc420_decompress() / avc444_decompress(). Subsequent YUV-RGB conversion (yuv420_context_decode -     avc420_yuv_to_rgb or avc444_yuv_to_rgb) consumes those surface-sized rectangles against the smaller     decoder-sized YUV planes, causing out-of-bounds reads on both axes.

    clamp() only limits rect.top/rect.bottom using MIN(context->height, srcHeight) where srcHeight is     h264->height (surface height on FFmpeg/OpenH264/MediaCodec paths). It does not clamp rect.left/rect.right.
    check_rect() is only invoked on the YUV444 combine path, not on the AVC420/AVC444 RGB conversion paths.
    (CVE-2026-55192)

    Heap-buffer-overflow write in TS Gateway RPC fragment receive due to uncapped bind_ack max_xmit_frag

    On TS Gateway connections, rpc->max_recv_frag is initialized to 0x0FF8 (4088) and ReceiveFragment is     allocated to that size. In rpc_bind.c, the client assigns rpc->max_recv_frag =     header.bind_ack.max_xmit_frag from the server without an upper bound. A malicious gateway can set     max_xmit_frag = 0xFFFF while ReceiveFragment is never resized.

    Later, rpc_client.c rejects fragments with if (header.frag_length > rpc->max_recv_frag). When both values     are 65535, the check passes (65535 > 65535 is false). The receive loop then calls rpc_channel_read() -     BIO_read() into the fixed 4088-byte ReceiveFragment, writing up to 65535 bytes and overflowing by up to     61447 attacker-controlled bytes. (CVE-2026-55193)

    Heap-buffer-overflow write in TS Gateway RPC RESPONSE reassembly due to alloc_hint capacity mismatch

    In rpc_client_recv_fragment(), when reassembling a PTYPE_RESPONSE PDU, the client calls     Stream_EnsureCapacity(pdu->s, response->alloc_hint) using only the server-declared alloc_hint.
    Stream_EnsureCapacity() returns success if the existing capacity is already >= alloc_hint, without     considering the current write offset or the actual stub length about to be copied.

    A malicious gateway can set a small alloc_hint (e.g. 100) while sending a large fragment (frag_length =     6000, yielding StubLength [?] 5968). The 4096-byte reassembly buffer is not grown, and     Stream_Write(pdu->s, ..., StubLength) copies attacker-controlled stub data past the end of the heap     allocation. On default builds this may abort via WINPR_ASSERT; on Release builds (NDEBUG) the assert is     elided and the overflow becomes an exploitable heap write.

    This is distinct from the separate ReceiveFragment / bind_ack max_xmit_frag issue (different buffer and     code path in the same gateway module). (CVE-2026-55194)

    Out-of-bounds read in glyph_cache_get via crafted glyph fragments

    A malicious RDP server can trigger an out-of-bounds heap read in a FreeRDP client through the glyph cache.
    glyph_cache_get() bounds-checks the index with > where it should use >= -- the sibling glyph_cache_put()     already gets it right. Since the cache's entries array holds exactly number pointers, an index equal to     number slips past the check and reads one slot past the end, which the caller then dereferences as a     glyph. It's the read-side twin of CVE-2020-11098 (the write side was fixed back in 2.1.2; the read side     never was), and it's still present in 3.25.0 and master. (CVE-2026-55564)

    Integer Overflow in freerdp_image_copy_from_icon_data Bypasses Bounds Check (CVE-2026-55648)

    Heap out-of-bounds write in FreeRDP RemoteFX (RFX) Cache Bitmap V3 decode - malicious RDP server achieves     controlled `$pc` in a connecting client (CVE-2026-55827)

    FreeRDP before 3.22.0 contains a use-after-free vulnerability in dvcman_channel_close and     dvcman_call_on_receive due to improper synchronization of channel_callback access. A malicious RDP server     can trigger a race condition by sending DYNVC_DATA and DYNVC_CLOSE messages concurrently, causing heap-     use-after-free in the drdynvc client thread and potentially enabling remote code execution or denial of     service. (CVE-2026-56297)

    Out-of-bounds read in the camera device enumerator server (rdpecam) via unterminated DeviceName /     VirtualChannelName (CVE-2026-57157)

    planar_decompress_plane_rle_only: heap OOB read -- incomplete fix for CVE-2026-23530

    The fix for CVE-2026-23530 (GHSA-r4hv-852m-fq7p) correctly adds dimension guardsat the entry point of     freerdp_bitmap_decompress_planar but is incomplete in scope.planar_decompress_plane_rle_only dereferences
    *srcp before validating thatsrcp is within SrcSize. A malicious server can reach this path via a     truncatedRLE planar payload in RDPGFX_CMDID_WIRETOSURFACE_1. (CVE-2026-57158)

Tenable has extracted the preceding description block directly from the tested product security advisory.

Note that Nessus has not tested for these issues but has instead relied only on the application's self-reported version number.

The Linux/Unix host has one or more packages installed that are impacted by a vulnerability without a vendor supplied patch available.

  - 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. (CVE-2026-55564)

Note that Nessus relies on the presence of the package as reported by the vendor.

ID	Name	Product	Family	Type	Severity
332057	Amazon Linux 2 : freerdp, --advisory ALAS2-2026-3840 (ALAS-2026-3840)	Nessus	Amazon Linux Local Security Checks	Local	high
331994	Amazon Linux 2023 : freerdp, freerdp-devel, freerdp-libs (ALAS2023-2026-2012)	Nessus	Amazon Linux Local Security Checks	Local	high
325536	Linux Distros Unpatched Vulnerability : CVE-2026-55564	Nessus	Misc.	Local	medium

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