From: Nick Wellnhofer <wellnhofer@aevum.de>
Date: Tue, 17 Dec 2024 15:56:21 +0100
Subject: [CVE-2025-24855] Fix use-after-free of XPath context node
Origin: https://gitlab.gnome.org/GNOME/libxslt/-/commit/c7c7f1f78dd202a053996fcefe57eb994aec8ef2
Bug-Debian: https://bugs.debian.org/1100566
Bug: https://gitlab.gnome.org/GNOME/libxslt/-/issues/128
Bug-Debian-Security: https://security-tracker.debian.org/tracker/CVE-2025-24855

There are several places where the XPath context node isn't restored
after modifying it, leading to use-after-free errors with nested XPath
evaluations and dynamically allocated context nodes.

Restore XPath context node in

- xsltNumberFormatGetValue
- xsltEvalXPathPredicate
- xsltEvalXPathStringNs
- xsltComputeSortResultInternal

In some places, the transformation context node was saved and restored
which shouldn't be necessary.

Thanks to Ivan Fratric for the report!

Fixes #128.
---
 libxslt/numbers.c   | 5 +++++
 libxslt/templates.c | 9 ++++++---
 libxslt/xsltutils.c | 4 ++--
 3 files changed, 13 insertions(+), 5 deletions(-)

diff --git a/libxslt/numbers.c b/libxslt/numbers.c
index 0e1fa1368413..741124d1a7cf 100644
--- a/libxslt/numbers.c
+++ b/libxslt/numbers.c
@@ -733,9 +733,12 @@ xsltNumberFormatGetValue(xmlXPathContextPtr context,
     int amount = 0;
     xmlBufferPtr pattern;
     xmlXPathObjectPtr obj;
+    xmlNodePtr oldNode;
 
     pattern = xmlBufferCreate();
     if (pattern != NULL) {
+        oldNode = context->node;
+
 	xmlBufferCCat(pattern, "number(");
 	xmlBufferCat(pattern, value);
 	xmlBufferCCat(pattern, ")");
@@ -748,6 +751,8 @@ xsltNumberFormatGetValue(xmlXPathContextPtr context,
 	    xmlXPathFreeObject(obj);
 	}
 	xmlBufferFree(pattern);
+
+        context->node = oldNode;
     }
     return amount;
 }
diff --git a/libxslt/templates.c b/libxslt/templates.c
index f08b9bda418f..1c8d96e26e95 100644
--- a/libxslt/templates.c
+++ b/libxslt/templates.c
@@ -61,6 +61,7 @@ xsltEvalXPathPredicate(xsltTransformContextPtr ctxt, xmlXPathCompExprPtr comp,
     int oldNsNr;
     xmlNsPtr *oldNamespaces;
     xmlNodePtr oldInst;
+    xmlNodePtr oldNode;
     int oldProximityPosition, oldContextSize;
 
     if ((ctxt == NULL) || (ctxt->inst == NULL)) {
@@ -69,6 +70,7 @@ xsltEvalXPathPredicate(xsltTransformContextPtr ctxt, xmlXPathCompExprPtr comp,
         return(0);
     }
 
+    oldNode = ctxt->xpathCtxt->node;
     oldContextSize = ctxt->xpathCtxt->contextSize;
     oldProximityPosition = ctxt->xpathCtxt->proximityPosition;
     oldNsNr = ctxt->xpathCtxt->nsNr;
@@ -96,8 +98,9 @@ xsltEvalXPathPredicate(xsltTransformContextPtr ctxt, xmlXPathCompExprPtr comp,
 	ctxt->state = XSLT_STATE_STOPPED;
 	ret = 0;
     }
-    ctxt->xpathCtxt->nsNr = oldNsNr;
 
+    ctxt->xpathCtxt->node = oldNode;
+    ctxt->xpathCtxt->nsNr = oldNsNr;
     ctxt->xpathCtxt->namespaces = oldNamespaces;
     ctxt->inst = oldInst;
     ctxt->xpathCtxt->contextSize = oldContextSize;
@@ -137,7 +140,7 @@ xsltEvalXPathStringNs(xsltTransformContextPtr ctxt, xmlXPathCompExprPtr comp,
     }
 
     oldInst = ctxt->inst;
-    oldNode = ctxt->node;
+    oldNode = ctxt->xpathCtxt->node;
     oldPos = ctxt->xpathCtxt->proximityPosition;
     oldSize = ctxt->xpathCtxt->contextSize;
     oldNsNr = ctxt->xpathCtxt->nsNr;
@@ -167,7 +170,7 @@ xsltEvalXPathStringNs(xsltTransformContextPtr ctxt, xmlXPathCompExprPtr comp,
 	 "xsltEvalXPathString: returns %s\n", ret));
 #endif
     ctxt->inst = oldInst;
-    ctxt->node = oldNode;
+    ctxt->xpathCtxt->node = oldNode;
     ctxt->xpathCtxt->contextSize = oldSize;
     ctxt->xpathCtxt->proximityPosition = oldPos;
     ctxt->xpathCtxt->nsNr = oldNsNr;
diff --git a/libxslt/xsltutils.c b/libxslt/xsltutils.c
index 0e9dc62f5fc3..a20da9618228 100644
--- a/libxslt/xsltutils.c
+++ b/libxslt/xsltutils.c
@@ -1065,8 +1065,8 @@ xsltComputeSortResultInternal(xsltTransformContextPtr ctxt, xmlNodePtr sort,
 	return(NULL);
     }
 
-    oldNode = ctxt->node;
     oldInst = ctxt->inst;
+    oldNode = ctxt->xpathCtxt->node;
     oldPos = ctxt->xpathCtxt->proximityPosition;
     oldSize = ctxt->xpathCtxt->contextSize;
     oldNsNr = ctxt->xpathCtxt->nsNr;
@@ -1137,8 +1137,8 @@ xsltComputeSortResultInternal(xsltTransformContextPtr ctxt, xmlNodePtr sort,
 	    results[i] = NULL;
 	}
     }
-    ctxt->node = oldNode;
     ctxt->inst = oldInst;
+    ctxt->xpathCtxt->node = oldNode;
     ctxt->xpathCtxt->contextSize = oldSize;
     ctxt->xpathCtxt->proximityPosition = oldPos;
     ctxt->xpathCtxt->nsNr = oldNsNr;
-- 
2.47.2