CVE-2026-102555

A flaw was found in libsoup. The soup_uri_decode_data_uri() function incorrectly treated base64 data-URI payloads as NUL-terminated strings when calling g_base64_decode_inplace(). If the percent-decoded payload contained embedded NUL bytes, the decoded length could remain uninitialized and be used as the size of the returned GBytes. This can lead to an out-of-bounds read or application crash when processing a crafted data URI.

Libsoup is an HTTP library implementation in C. It was originally part of a SOAP (Simple Object Access Protocol) implementation called Soup, but the SOAP and non-SOAP parts have now been split into separate packages. libsoup uses the Glib main loop and is designed to work well with GTK applications. This enables GNOME applications to access HTTP servers on the network in a completely asynchronous fashion, very similar to the Gtk+ programming model (a synchronous operation mode is also supported for those who want it), but the SOAP parts were removed long ago.

Security Fix(es):

• libsoup: libsoup: Heap buffer overflow via uninitialized length in data-URI base64 decoding (CVE-2026-102555)
• libsoup: libsoup: Heap buffer overflow from WebSocket Pong signal type confusion (CVE-2026-102556)
• libsoup: libsoup: Heap buffer overflow during WebSocket message reassembly (CVE-2026-102557)
• libsoup: libsoup: Heap buffer overflow during WebSocket receive-buffer growth (CVE-2026-102558)
• libsoup: libsoup: Heap buffer overflow during WebSocket client-frame masking (CVE-2026-102559)
• libsoup: libsoup: Heap buffer overflow during outgoing permessage-deflate buffer growth (CVE-2026-102560)

For more details about the security issue(s), including the impact, a CVSS score, acknowledgments, and other related information, refer to the CVE page(s) listed in the References section.

A flaw was found in libsoup. The soup_uri_decode_data_uri() function incorrectly treated base64 data-URI payloads as NUL-terminated strings when calling g_base64_decode_inplace(). If the percent-decoded payload contained embedded NUL bytes, the decoded length could remain uninitialized and be used as the size of the returned GBytes. This can lead to an out-of-bounds read or application crash when processing a crafted data URI.

• CVE-2026-102555: decode base64 data: URI content with g_base64_decode_step() over the real buffer length in soup_request_data_send(), so a percent-encoded NUL no longer truncates the payload, leaks the decode buffer and raises a GLib-CRITICAL
• CVE-2026-102556: emit the WebSocket ::pong signal with a GBytes, as the signal and the public header have always declared, instead of a GByteArray, removing the type confusion a crafted Pong frame could turn into heap corruption in any handler that honours the documented API
• CVE-2026-102557: cap a reassembled WebSocket message at what a GByteArray can hold before each fragment is appended in process_contents(), so a run of fragments can no longer truncate the guint size passed to g_byte_array_sized_new()/g_byte_array_append() while the full length is used
• CVE-2026-102558: reject an incoming frame whose declared payload exceeds what the receive buffer can represent as soon as the header is parsed, so the incoming GByteArray can no longer grow until g_byte_array_set_size() wraps and the read writes past the allocation
• CVE-2026-102559: reject an outgoing payload above MAX_OUTGOING_PAYLOAD_SIZE in send_message(), both before and after extensions have processed it, so a masked client frame can no longer be built in a truncated GByteArray while xor_with_mask() writes the full payload length past the allocation
• CVE-2026-102560: refuse an outgoing permessage-deflate payload whose deflateBound() exceeds G_MAXUINT and bound every incremental buffer growth, so a truncated bound can no longer let zlib write past the allocated GByteArray

• CVE-2026-102555: decode base64 data: URI content with g_base64_decode_step() over the real buffer length in soup_request_data_send(), so a percent-encoded NUL no longer truncates the payload, leaks the decode buffer and raises a GLib-CRITICAL
• CVE-2026-102556: emit the WebSocket ::pong signal with a GBytes, as the signal and the public header have always declared, instead of a GByteArray, removing the type confusion a crafted Pong frame could turn into heap corruption in any handler that honours the documented API
• CVE-2026-102557: cap a reassembled WebSocket message at what a GByteArray can hold before each fragment is appended in process_contents(), so a run of fragments can no longer truncate the guint size passed to g_byte_array_sized_new()/g_byte_array_append() while the full length is used
• CVE-2026-102558: reject an incoming frame whose declared payload exceeds what the receive buffer can represent as soon as the header is parsed, so the incoming GByteArray can no longer grow until g_byte_array_set_size() wraps and the read writes past the allocation
• CVE-2026-102559: reject an outgoing payload above MAX_OUTGOING_PAYLOAD_SIZE in send_message(), both before and after extensions have processed it, so a masked client frame can no longer be built in a truncated GByteArray while xor_with_mask() writes the full payload length past the allocation
• CVE-2026-102560: refuse an outgoing permessage-deflate payload whose deflateBound() exceeds G_MAXUINT and bound every incremental buffer growth, so a truncated bound can no longer let zlib write past the allocated GByteArray

This update for libsoup fixes the following issues:

• CVE-2026-12547: Header "Proxy-Authorization" leads to credentials being send to different proxy after proxy switch (bsc#1272195).
• CVE-2026-12548: out-of-bounds read in multipart body parser due to an integer truncation (bsc#1272196).
• CVE-2026-15711: SoupWebsocketConnection: WebSocket remote denial of service via oversized control frame protocol violation (bsc#1271446).
• CVE-2026-15712: SoupClientMessageIOHTTP2: HTTP/2 GOAWAY frame parsing heap buffer over-read via invalid NUL- termination assumption (bsc#1271447).
• CVE-2026-15713: SoupCache: libsoup: HTTP/2 frame window exhaustion remote denial of service via memory leak (bsc#1271448).
• CVE-2026-15714: SoupMultipartInputStream: libsoup: Out-of-bounds read in soup_multipart_input_stream_read_headers via an oversized multipart boundary string (bsc#1271449).
• CVE-2026-66339: proxy credentials leak to destination server via Proxy-Authorization header in CONNECT tunnels (bsc#1273156).
• CVE-2026-102555: Heap buffer overflow via uninitialized length in data-URI base64 decoding (bsc#1283299).
• CVE-2026-102556: Heap buffer overflow from WebSocket Pong signal type confusion (bsc#1283300).
• CVE-2026-102557: Heap buffer overflow during WebSocket message reassembly (bsc#1283301).
• CVE-2026-102558: Heap buffer overflow during WebSocket receive-buffer growth (bsc#1283302).
• CVE-2026-102559: Heap buffer overflow during WebSocket client-frame masking (bsc#1283303).
• CVE-2026-102560: Heap buffer overflow during outgoing permessage-deflate buffer growth (bsc#1283304).
• CVE-2026-103399: incomplete request body draining in HTTP/1.x early responses can allow HTTP request smuggling (bsc#1283831).

Root has patched CVE-2026-102555 in the libsoup3 package for Root:Debian:13. Multiple fixed versions available.

This update for libsoup fixes the following issues:

• CVE-2026-12547: Header "Proxy-Authorization" leads to credentials being send to different proxy after proxy switch (bsc#1272195).
• CVE-2026-12548: out-of-bounds read in multipart body parser due to an integer truncation (bsc#1272196).
• CVE-2026-15711: SoupWebsocketConnection: WebSocket remote denial of service via oversized control frame protocol violation (bsc#1271446).
• CVE-2026-15712: SoupClientMessageIOHTTP2: HTTP/2 GOAWAY frame parsing heap buffer over-read via invalid NUL- termination assumption (bsc#1271447).
• CVE-2026-15713: SoupCache: libsoup: HTTP/2 frame window exhaustion remote denial of service via memory leak (bsc#1271448).
• CVE-2026-15714: SoupMultipartInputStream: libsoup: Out-of-bounds read in soup_multipart_input_stream_read_headers via an oversized multipart boundary string (bsc#1271449).
• CVE-2026-66339: proxy credentials leak to destination server via Proxy-Authorization header in CONNECT tunnels (bsc#1273156).
• CVE-2026-102555: Heap buffer overflow via uninitialized length in data-URI base64 decoding (bsc#1283299).
• CVE-2026-102556: Heap buffer overflow from WebSocket Pong signal type confusion (bsc#1283300).
• CVE-2026-102557: Heap buffer overflow during WebSocket message reassembly (bsc#1283301).
• CVE-2026-102558: Heap buffer overflow during WebSocket receive-buffer growth (bsc#1283302).
• CVE-2026-102559: Heap buffer overflow during WebSocket client-frame masking (bsc#1283303).
• CVE-2026-102560: Heap buffer overflow during outgoing permessage-deflate buffer growth (bsc#1283304).
• CVE-2026-103399: incomplete request body draining in HTTP/1.x early responses can allow HTTP request smuggling (bsc#1283831).

This update for libsoup fixes the following issues:

• CVE-2026-12547: Header "Proxy-Authorization" leads to credentials being send to different proxy after proxy switch (bsc#1272195).
• CVE-2026-12548: out-of-bounds read in multipart body parser due to an integer truncation (bsc#1272196).
• CVE-2026-15711: SoupWebsocketConnection: WebSocket remote denial of service via oversized control frame protocol violation (bsc#1271446).
• CVE-2026-15712: SoupClientMessageIOHTTP2: HTTP/2 GOAWAY frame parsing heap buffer over-read via invalid NUL- termination assumption (bsc#1271447).
• CVE-2026-15713: SoupCache: libsoup: HTTP/2 frame window exhaustion remote denial of service via memory leak (bsc#1271448).
• CVE-2026-15714: SoupMultipartInputStream: libsoup: Out-of-bounds read in soup_multipart_input_stream_read_headers via an oversized multipart boundary string (bsc#1271449).
• CVE-2026-66339: proxy credentials leak to destination server via Proxy-Authorization header in CONNECT tunnels (bsc#1273156).
• CVE-2026-102555: Heap buffer overflow via uninitialized length in data-URI base64 decoding (bsc#1283299).
• CVE-2026-102556: Heap buffer overflow from WebSocket Pong signal type confusion (bsc#1283300).
• CVE-2026-102557: Heap buffer overflow during WebSocket message reassembly (bsc#1283301).
• CVE-2026-102558: Heap buffer overflow during WebSocket receive-buffer growth (bsc#1283302).
• CVE-2026-102559: Heap buffer overflow during WebSocket client-frame masking (bsc#1283303).
• CVE-2026-102560: Heap buffer overflow during outgoing permessage-deflate buffer growth (bsc#1283304).
• CVE-2026-103399: incomplete request body draining in HTTP/1.x early responses can allow HTTP request smuggling (bsc#1283831).

This update for libsoup fixes the following issues:

• CVE-2026-15713: SoupCache: libsoup: HTTP/2 frame window exhaustion remote denial of service via memory leak (bsc#1271448).
• CVE-2026-102555: Heap buffer overflow via uninitialized length in data-URI base64 decoding (bsc#1283299).
• CVE-2026-102556: Heap buffer overflow from WebSocket Pong signal type confusion (bsc#1283300).
• CVE-2026-102557: Heap buffer overflow during WebSocket message reassembly (bsc#1283301).
• CVE-2026-102558: Heap buffer overflow during WebSocket receive-buffer growth (bsc#1283302).
• CVE-2026-102559: Heap buffer overflow during WebSocket client-frame masking (bsc#1283303).
• CVE-2026-102560: Heap buffer overflow during outgoing permessage-deflate buffer growth (bsc#1283304).

This update for libsoup fixes the following issues:

• CVE-2026-15713: SoupCache: libsoup: HTTP/2 frame window exhaustion remote denial of service via memory leak (bsc#1271448).
• CVE-2026-102555: Heap buffer overflow via uninitialized length in data-URI base64 decoding (bsc#1283299).
• CVE-2026-102556: Heap buffer overflow from WebSocket Pong signal type confusion (bsc#1283300).
• CVE-2026-102557: Heap buffer overflow during WebSocket message reassembly (bsc#1283301).
• CVE-2026-102558: Heap buffer overflow during WebSocket receive-buffer growth (bsc#1283302).
• CVE-2026-102559: Heap buffer overflow during WebSocket client-frame masking (bsc#1283303).
• CVE-2026-102560: Heap buffer overflow during outgoing permessage-deflate buffer growth (bsc#1283304).

It was discovered that libsoup incorrectly handled certain WebSocket frames. A remote attacker could possibly use this issue to cause an application to crash or expose sensitive information. This issue only affected Ubuntu 22.04 LTS, Ubuntu 24.04 LTS, Ubuntu 26.04 LTS, and Ubuntu 26.10. (CVE-2026-12478)

It was discovered that libsoup incorrectly handled certain data URIs. A remote attacker could possibly use this issue to cause an application to crash or expose sensitive information. This issue only affected Ubuntu 22.04 LTS, Ubuntu 24.04 LTS, Ubuntu 26.04 LTS, and Ubuntu 26.10. (CVE-2026-102555)

It was discovered that libsoup incorrectly handled certain WebSocket messages. A remote attacker could possibly use this issue to cause an application to crash. This issue only affected Ubuntu 18.04 LTS, Ubuntu 20.04 LTS, Ubuntu 22.04 LTS, Ubuntu 24.04 LTS, Ubuntu 26.04 LTS, and Ubuntu 26.10. (CVE-2026-102556)

It was discovered that libsoup incorrectly handled fragmented WebSocket messages. A remote attacker could possibly use this issue to cause an application to crash. (CVE-2026-102557)

It was discovered that libsoup incorrectly handled certain WebSocket frames. A remote attacker could possibly use this issue to cause an application to crash. This issue only affected Ubuntu 18.04 LTS, Ubuntu 20.04 LTS, Ubuntu 22.04 LTS, Ubuntu 24.04 LTS, Ubuntu 26.04 LTS, and Ubuntu 26.10. (CVE-2026-102558)

It was discovered that libsoup incorrectly handled large WebSocket messages. An attacker could possibly use this issue to cause an application to crash. (CVE-2026-102559)

It was discovered that libsoup incorrectly handled compressed WebSocket messages. An attacker could possibly use this issue to cause an application to crash. This issue only affected Ubuntu 20.04 LTS, Ubuntu 22.04 LTS, Ubuntu 24.04 LTS, Ubuntu 26.04 LTS, and Ubuntu 26.10. (CVE-2026-102560)

It was discovered that libsoup did not properly handle certain HTTP requests. A remote attacker could possibly use this issue to inject arbitrary HTTP requests. (CVE-2026-103399)

It was discovered that libsoup incorrectly handled proxy credentials. A remote attacker could possibly use this issue to obtain sensitive information. (CVE-2026-12547)

It was discovered that libsoup incorrectly handled multipart messages. A remote attacker could possibly use this issue to cause an application to crash or obtain sensitive information. (CVE-2026-12548)