CVE-2023-51766

Exim is a message transfer agent (MTA) developed at the University of Cambridge for use on Unix systems connected to the Internet. It is freely available under the terms of the GNU General Public Licence. In style it is similar to Smail 3, but its facilities are more general. There is a great deal of flexibility in the way mail can be routed, and there are extensive facilities for checking incoming mail. Exim can be installed in place of sendmail, although the configuration of exim is quite different to that of sendmail.

Security Fix(es):

A vulnerability was found in Exim and classified as problematic. This issue affects some unknown processing of the component Regex Handler. The manipulation leads to use after free. The name of the patch is 4e9ed49f8f12eb331b29bd5b6dc3693c520fddc2. It is recommended to apply a patch to fix this issue. The identifier VDB-211073 was assigned to this vulnerability.(CVE-2022-3559)

Exim before 4.97.1 allows SMTP smuggling in certain PIPELINING/CHUNKING configurations. Remote attackers can use a published exploitation technique to inject e-mail messages with a spoofed MAIL FROM address, allowing bypass of an SPF protection mechanism. This occurs because Exim supports <LF>.<CR><LF> but some other popular e-mail servers do not.(CVE-2023-51766)

Exim is a message transfer agent (MTA) developed at the University of Cambridge for use on Unix systems connected to the Internet. It is freely available under the terms of the GNU General Public Licence. In style it is similar to Smail 3, but its facilities are more general. There is a great deal of flexibility in the way mail can be routed, and there are extensive facilities for checking incoming mail. Exim can be installed in place of sendmail, although the configuration of exim is quite different to that of sendmail.

Security Fix(es):

Exim before 4.97.1 allows SMTP smuggling in certain PIPELINING/CHUNKING configurations. Remote attackers can use a published exploitation technique to inject e-mail messages with a spoofed MAIL FROM address, allowing bypass of an SPF protection mechanism. This occurs because Exim supports <LF>.<CR><LF> but some other popular e-mail servers do not.(CVE-2023-51766)

Exim before 4.97.1 allows SMTP smuggling in certain PIPELINING/CHUNKING configurations. Remote attackers can use a published exploitation technique to inject e-mail messages with a spoofed MAIL FROM address, allowing bypass of an SPF protection mechanism. This occurs because Exim supports <LF>.<CR><LF> but some other popular e-mail servers do not.

• SECURITY UPDATE: SMTP smuggling because of <LF>.<CR><LF> support
  • debian/patches/CVE-2023-51766.patch: reject "dot, LF" as ending data phase. Testcase for "smtp smuggling".
  • CVE-2023-51766

• SECURITY UPDATE: SMTP smuggling because of <LF>.<CR><LF> support
  • debian/patches/CVE-2023-51766.patch: reject "dot, LF" as ending data phase. Testcase for "smtp smuggling".
  • CVE-2023-51766

Exim before 4.97.1 allows SMTP smuggling in certain PIPELINING/CHUNKING configurations. Remote attackers can use a published exploitation technique to inject e-mail messages with a spoofed MAIL FROM address, allowing bypass of an SPF protection mechanism. This occurs because Exim supports <LF>.<CR><LF> but some other popular e-mail servers do not.

This update for exim fixes the following issues:

exim was updated to 4.97.1 (boo#1218387, CVE-2023-51766):

• Fixes for the smtp protocol smuggling (CVE-2023-51766)

exim was updated to exim 4.96:

• Move from using the pcre library to pcre2.
• Constification work in the filters module required a major version bump for the local-scan API. Specifically, the 'headers_charset' global which is visible via the API is now const and may therefore not be modified by local-scan code.
• Bug 2819: speed up command-line messages being read in. Previously a time check was being done for every character; replace that with one per buffer.
• Bug 2815: Fix ALPN sent by server under OpenSSL. Previously the string sent was prefixed with a length byte.
• Change the SMTP feature name for pipelining connect to be compliant with RFC 5321. Previously Dovecot (at least) would log errors during submission.
• Fix macro-definition during '-be' expansion testing. The move to write-protected store for macros had not accounted for these runtime additions; fix by removing this protection for '-be' mode.
• Convert all uses of select() to poll().
• Fix use of $sender_host_name in daemon process. When used in certain main-section options or in a connect ACL, the value from the first ever connection was never replaced for subsequent connections.
• Bug 2838: Fix for i32lp64 hard-align platforms
• Bug 2845: Fix handling of tls_require_ciphers for OpenSSL when a value with underbars is given.
• Bug 1895: TLS: Deprecate RFC 5114 Diffie-Hellman parameters.
• Debugging initiated by an ACL control now continues through into routing and transport processes.
• The 'expand' debug selector now gives more detail, specifically on the result of expansion operators and items.
• Bug 2751: Fix include_directory in redirect routers. Previously a bad comparison between the option value and the name of the file to be included was done, and a mismatch was wrongly identified.
• Support for Berkeley DB versions 1 and 2 is withdrawn.
• When built with NDBM for hints DB's check for nonexistence of a name supplied as the db file-pair basename.
• Remove the 'allow_insecure_tainted_data' main config option and the 'taint' log_selector.
• Fix static address-list lookups to properly return the matched item. Previously only the domain part was returned.
• The ${run} expansion item now expands its command string elements after splitting. Previously it was before; the new ordering makes handling zero-length arguments simpler.
• Taint-check exec arguments for transport-initiated external processes. Previously, tainted values could be used. This affects 'pipe', 'lmtp' and 'queryprogram' transport, transport-filter, and ETRN commands. The ${run} expansion is also affected: in 'preexpand' mode no part of the command line may be tainted, in default mode the executable name may not be tainted.
• Fix CHUNKING on a continued-transport. Previously the usabilility of the facility was not passed across execs, and only the first message passed over a connection could use BDAT; any further ones using DATA.
• Support the PIPECONNECT facility in the smtp transport when the helo_data uses $sending_ip_address and an interface is specified.
• OpenSSL: fix transport-required OCSP stapling verification under session resumption.
• TLS resumption: the key for session lookup in the client now includes more info that a server could potentially use in configuring a TLS session, avoiding oferring mismatching sessions to such a server.
• Fix string_copyn() for limit greater than actual string length.
• Bug 2886: GnuTLS: Do not free the cached creds on transport connection close; it may be needed for a subsequent connection.
• Fix CHUNKING for a second message on a connection when the first was rejected.
• Fix…

These are all security issues fixed in the exim-4.97.1-1.1 package on the GA media of openSUSE Tumbleweed.

It was discovered that Exim incorrectly handled certain requests. A remote attacker could possibly use a published exploitation technique to inject e-mail messages with a spoofed MAIL FROM address, allowing bypass of an SPF protection mechanism.

Timo Longin discovered that Exim incorrectly handled certain SMTP messages in PIPELINING/CHUNKING configurations. A remote attacker could possibly use this issue to perform SMTP smuggling. This issue only affected Ubuntu 14.04 LTS. (CVE-2023-51766)

It was discovered that Exim incorrectly handled certain malformed JSON data in headers. A remote attacker could possibly use this issue to crash Exim, resulting in a denial of service, or execute arbitrary code. This issue only affected Ubuntu 20.04 LTS. (CVE-2026-40685)

It was discovered that Exim incorrectly handled certain malformed UTF-8 headers. A remote attacker could possibly use this issue to obtain sensitive information. This issue only affected Ubuntu 20.04 LTS. (CVE-2026-40686)

It was discovered that Exim incorrectly handled certain SPA resources. A remote attacker could possibly use this issue to crash Exim, resulting in a denial of service, or obtain sensitive information. This issue only affected Ubuntu 20.04 LTS. (CVE-2026-40687)

It was discovered that Exim incorrectly handled certain CHUNKING transfers in some GnuTLS configurations. A remote attacker could possibly use this issue to crash Exim, resulting in a denial of service, or execute arbitrary code. This issue only affected Ubuntu 20.04 LTS. (CVE-2026-45185)

Warisjeet Singh discovered that Exim incorrectly handled certain proxy connections in builds with proxy support enabled. A remote attacker could possibly use this issue to obtain sensitive information. This issue only affected Ubuntu 16.04 LTS, Ubuntu 18.04 LTS, and Ubuntu 20.04 LTS. (CVE-2026-48840)