Libevent vulnerabilities

The search_make_new function in evdns.c in libevent before version 2.1.6-beta allows attackers to cause a denial of service (out-of-bounds read) via an empty hostname.

A stack-based buffer overflow in the evutil_parse_sockaddr_port function in evutil.c in libevent before version 2.1.6-beta allows attackers to cause a denial of service (segmentation fault) via vectors involving a long string in brackets in the ip_as_string argument.

Multiple integer overflows in the evbuffer API in Libevent 2.0.x before 2.0.22 and 2.1.x before 2.1.5-beta may allow attackers to cause a denial of service or possibly have other unspecified impact via 'insanely large inputs'.

Multiple integer overflows in the evbuffer API in Libevent 1.4.x before 1.4.15, 2.0.x before 2.0.22, and 2.1.x before 2.1.5-beta allow context-dependent attackers to cause a denial of service or possibly have other unspecified impact via 'insanely large inputs'.

A vulnerability in Libevent before versions 2.1.13 and 2.2.2-alpha includes two HTTP parsing weaknesses in http.c. evhttp_decode_uri_internal decodes percent-encoded %00 bytes into literal NUL characters, which can cause path truncation and bypass validation. evhttp_header_is_valid_value also accepts obsolete line folding in header values containing CR or LF, allowing a proxy and libevent to interpret headers differently.

Libevent before versions 2.1.13 and 2.2.2-alpha inconsistently handles duplicate Transfer-Encoding headers, comma-separated values, and bare line feeds in chunked framing. This can lead to request desynchronization and request smuggling by an unauthenticated remote attacker when deployed behind a proxy.

The name_parse function in evdns.c in libevent before version 2.1.6-beta allows remote attackers to have unspecified impact via vectors involving the label_len variable, leading to an out-of-bounds stack read.

Libevent is an event notification library. From 2.2.0-alpha-dev until 2.2.2-alpha, the libevent WebSocket server in ws.c accumulates fragmented frames in evws->incomplete_frames without enforcing a total message-size limit. An unauthenticated remote client can repeatedly send fragmented WebSocket frames below WS_MAX_RECV_FRAME_SZ with FIN=0, causing the evbuffer to grow without bound until the process or host exhausts memory. This issue is fixed in version 2.2.2-alpha.

Libevent prior to 2.1.13 and 2.2.2-alpha has a heap out-of-bounds write in bufferevent_sock.c when bufferevent_socket_set_conn_address_ copies a kernel-supplied AF_UNIX peer address into bufferevent_private.conn_address. Release builds compiled with NDEBUG disable the EVUTIL_ASSERT length guard, and the evhttp accept path can pass a 110-byte sockaddr from accept() into the 28-byte field. An unauthenticated local peer able to connect to an AF_UNIX listener can overwrite the adjacent dns_request pointer and heap data, causing memory corruption with confidentiality, integrity, and availability impact. This issue is fixed in versions 2.1.13 and 2.2.2-alpha.

Libevent prior to 2.1.13 and 2.2.2-alpha has an off-by-one stack buffer overflow in evdns.c when dnsname_to_labels formats a name-bearing DNS record at the end of the 64 KB stack buffer allocated by evdns_server_request_format_response. The final-label check permits j plus label_len plus one to equal buf_len, after which the terminating null byte is written to buf[buf_len]. A crafted DNS server response containing PTR, CNAME, MX, NS, or SOA data can trigger the one-byte out-of-bounds write and crash or corrupt the process. This issue is fixed in versions 2.1.13 and 2.2.2-alpha.

Libevent prior to 2.1.13 and 2.2.2-alpha has an incorrect integer conversion in event_tagging.c when evtag_unmarshal_header uses evtag_decode_int to decode an attacker-controlled uint32 payload length and returns it as a signed int. Values above INT_MAX become negative or truncated, and evtag_unmarshal_string can use the converted value in allocation sizing, producing a wrapped large allocation request and denial of service. This issue is fixed in versions 2.1.13 and 2.2.2-alpha.

Libevent prior to 2.1.13 and 2.2.2-alpha can read beyond a contiguous evbuffer region in event_tagging.c when decode_tag_internal requests at most five bytes from evbuffer_pullup but iterates using the full logical buffer length. A fragmented evbuffer containing a six-byte malformed tag can therefore advance past the pullup window and trigger an out-of-bounds read, which can crash a process that decodes attacker-controlled tagged RPC data. This issue is fixed in versions 2.1.13 and 2.2.2-alpha.

Libevent is an event notification library. Prior to 2.1.13 and 2.2.2-alpha, libevent has a use-after-free in buffer.c when evbuffer_add_buffer_reference processes an output buffer whose out_total_len is zero. evbuffer_free_all_chains frees the initial empty chain without resetting outbuf->first, outbuf->last, or outbuf->last_with_datap, and APPEND_CHAIN_MULTICAST subsequently dereferences the dangling chain pointer. A caller that can drive this buffer state can cause memory corruption or a process crash. This issue is fixed in versions 2.1.13 and 2.2.2-alpha.

Libevent before 2.2.2-alpha can dereference invalid list pointers in ws.c when evws_new_session enters its error path after evhttp_start_ws_ succeeds but bufferevent_enable_locking_ fails. This can cause a process crash.

Libevent before 2.1.13 and 2.2.2-alpha processes chunked HTTP trailers and merges them into request headers. An unauthenticated remote attacker can place security-sensitive fields in trailers, causing header smuggling, authorization bypass, proxy-header spoofing, or cache poisoning.