new file mode 100644
@@ -0,0 +1,63 @@
+From f234bdf5c0f94b681312452fcd5e36968221fa04 Mon Sep 17 00:00:00 2001
+From: Mark Adler <git@madler.net>
+Date: Sun, 21 Dec 2025 18:17:56 -0800
+Subject: [PATCH] Check for negative lengths in crc32_combine functions.
+
+Though zlib.h says that len2 must be non-negative, this avoids the
+possibility of an accidental infinite loop.
+
+Upstream-Status: Backport [https://github.com/madler/zlib/commit/ba829a458576d1ff0f26fc7230c6de816d1f6a77]
+CVE: CVE-2026-27171
+
+Signed-off-by: Hugo SIMELIERE <hsimeliere.opensource@witekio.com>
+---
+ crc32.c | 4 ++++
+ zlib.h | 4 ++--
+ 2 files changed, 6 insertions(+), 2 deletions(-)
+
+diff --git a/crc32.c b/crc32.c
+index 6c38f5c..33d8c79 100644
+--- a/crc32.c
++++ b/crc32.c
+@@ -1019,6 +1019,8 @@ unsigned long ZEXPORT crc32(unsigned long crc, const unsigned char FAR *buf,
+
+ /* ========================================================================= */
+ uLong ZEXPORT crc32_combine64(uLong crc1, uLong crc2, z_off64_t len2) {
++ if (len2 < 0)
++ return 0;
+ #ifdef DYNAMIC_CRC_TABLE
+ once(&made, make_crc_table);
+ #endif /* DYNAMIC_CRC_TABLE */
+@@ -1032,6 +1034,8 @@ uLong ZEXPORT crc32_combine(uLong crc1, uLong crc2, z_off_t len2) {
+
+ /* ========================================================================= */
+ uLong ZEXPORT crc32_combine_gen64(z_off64_t len2) {
++ if (len2 < 0)
++ return 0;
+ #ifdef DYNAMIC_CRC_TABLE
+ once(&made, make_crc_table);
+ #endif /* DYNAMIC_CRC_TABLE */
+diff --git a/zlib.h b/zlib.h
+index 8d4b932..8c7f8ac 100644
+--- a/zlib.h
++++ b/zlib.h
+@@ -1758,14 +1758,14 @@ ZEXTERN uLong ZEXPORT crc32_combine(uLong crc1, uLong crc2, z_off_t len2);
+ seq1 and seq2 with lengths len1 and len2, CRC-32 check values were
+ calculated for each, crc1 and crc2. crc32_combine() returns the CRC-32
+ check value of seq1 and seq2 concatenated, requiring only crc1, crc2, and
+- len2. len2 must be non-negative.
++ len2. len2 must be non-negative, otherwise zero is returned.
+ */
+
+ /*
+ ZEXTERN uLong ZEXPORT crc32_combine_gen(z_off_t len2);
+
+ Return the operator corresponding to length len2, to be used with
+- crc32_combine_op(). len2 must be non-negative.
++ crc32_combine_op(). len2 must be non-negative, otherwise zero is returned.
+ */
+
+ ZEXTERN uLong ZEXPORT crc32_combine_op(uLong crc1, uLong crc2, uLong op);
+--
+2.43.0
+
@@ -10,6 +10,7 @@ LIC_FILES_CHKSUM = "file://zlib.h;beginline=6;endline=23;md5=5377232268e952e9ef6
SRC_URI = "https://zlib.net/${BP}.tar.gz \
file://0001-configure-Pass-LDFLAGS-to-link-tests.patch \
file://run-ptest \
+ file://CVE-2026-27171.patch \
"
UPSTREAM_CHECK_URI = "http://zlib.net/"