diff --git a/main/libspf2/APKBUILD b/main/libspf2/APKBUILD
index f38d3465e46..9c5e7122363 100644
--- a/main/libspf2/APKBUILD
+++ b/main/libspf2/APKBUILD
@@ -4,7 +4,7 @@
 pkgname=libspf2
 pkgver=1.2.11
 _commit=8131fe140704eaae695e76b5cd09e39bd1dd220b
-pkgrel=2
+pkgrel=3
 pkgdesc="Sender Policy Framework library, a part of the SPF/SRS protocol pair."
 url="https://www.libspf2.org/"
 arch="all"
@@ -13,6 +13,7 @@ subpackages="$pkgname-dev $pkgname-tools"
 makedepends="autoconf automake libtool"
 options="!check" # no test suite
 source="$pkgname-$pkgver.tar.gz::https://github.com/shevek/libspf2/archive/$_commit.tar.gz
+	CVE-2023-42118.patch
 	00001.patch
 	00002.patch
 	netdb_success.patch
@@ -22,6 +23,8 @@ source="$pkgname-$pkgver.tar.gz::https://github.com/shevek/libspf2/archive/$_com
 builddir="$srcdir/$pkgname-$_commit"
 
 # secfixes:
+#   1.2.11-r3:
+#     - CVE-2023-42118
 #   1.2.11-r0:
 #     - CVE-2021-33912
 #     - CVE-2021-33913
@@ -60,6 +63,7 @@ tools() {
 
 sha512sums="
 bbc8b053aa5dc960be7a31ee4d4385d9ed7f42a7c998a392626610de9a7dd9f95f16ad309990d0118f1eab3bed49189ed1be9c30d291c0ca54541677a968ceb3  libspf2-1.2.11.tar.gz
+9e17764f24de8147a27a41a5aeaf0554af6f434c04aa5ddea56fd4692f208c1c2576acd28ff06a2be6ff32945f5a441405b2ebb2f393c6a571e34723b023b1f5  CVE-2023-42118.patch
 3b9bff9b5a5b95f6722f86a43373b0c84cbb79a4509cf0c73486612c0a1b33587bb0b42966b0d2e3a317e4d7a730091fa444bd1258afd06bb3553c4a96d3ee34  00001.patch
 18ddfe106b652e2fb9e36a9f1743fc7cecf38530da65a06ac892b60d2c430aaad657f5653495950d4af4b9833826366b79e629937498e5ce7f6af716303221c4  00002.patch
 033dd1e959004f7a1026fb1de73813e934560101e04897297e468918ee28e4d7d0f271d6f05d984db22dd43e097f6aa133df18d11419b085d89db89b120750c9  netdb_success.patch
diff --git a/main/libspf2/CVE-2023-42118.patch b/main/libspf2/CVE-2023-42118.patch
new file mode 100644
index 00000000000..e13f3646da1
--- /dev/null
+++ b/main/libspf2/CVE-2023-42118.patch
@@ -0,0 +1,26 @@
+From c93823faef044150e1b232928d225ff5ff297e6c Mon Sep 17 00:00:00 2001
+From: Simon Arlott <sa.me.uk>
+Date: Sat, 30 Sep 2023 12:18:51 +0100
+Subject: [PATCH] Fix integer underflow
+
+---
+ src/libspf2/spf_compile.c | 6 +++++-
+ 1 file changed, 5 insertions(+), 1 deletion(-)
+
+diff --git a/src/libspf2/spf_compile.c b/src/libspf2/spf_compile.c
+index b08ffe2..d401028 100644
+--- a/src/libspf2/spf_compile.c
++++ b/src/libspf2/spf_compile.c
+@@ -455,7 +455,11 @@ SPF_c_parse_var(SPF_response_t *spf_response, SPF_data_var_t *data,
+ 			/* Magic numbers for x/Nc in gdb. */					\
+ 			data->ds.__unused0 = 0xba; data->ds.__unused1 = 0xbe;	\
+ 			dst = SPF_data_str( data );								\
+-			ds_avail = _avail - sizeof(SPF_data_t);					\
++			if ((_avail) < sizeof(SPF_data_t))						\
++				return SPF_response_add_error_ptr(spf_response,		\
++									SPF_E_BIG_STRING, NULL, src,	\
++								"Out of memory for string literal");\
++			ds_avail = (_avail) - sizeof(SPF_data_t);				\
+ 			ds_len = 0;												\
+ 		} while(0)
+