CVE-2021-20271 (published 2021-03-26T17:15Z)

A flaw was found in RPM's signature check functionality when reading a package file. This flaw allows an attacker who can convince a victim to install a seemingly verifiable package, whose signature header was modified, to cause RPM database corruption and execute code. The highest threat from this vulnerability is to data integrity, confidentiality, and system availability.

Severity: MEDIUM
CVSS v2 base score: 5.1 (AV:N/AC:H/Au:N/C:P/I:P/A:P)
CVSS v3 base score: 7.0, HIGH (CVSS:3.1/AV:L/AC:H/PR:N/UI:R/S:U/C:H/I:H/A:H)

Weakness information:
cwe_id: CWE-345
cwe_name: Insufficient Verification of Data Authenticity
description: The product does not sufficiently verify the origin or authenticity of data, in a way that causes it to accept invalid data.
extended_description: 
            
         
         

Fix information:
repo_url: https://github.com/rpm-software-management/rpm
commit_details: repo_url: https://github.com/rpm-software-management/rpm
author: Panu Matilainen
author_date: 2021-03-04 13:21:19+02:00
msg: Be much more careful about copying data from the signature header

Only look for known tags, and ensure correct type and size where known
before copying over. Bump the old arbitrary 16k count limit to 16M limit
though, it's not inconceivable that a package could have that many files.
While at it, ensure none of these tags exist in the main header,
which would confuse us greatly.

This is optimized for backporting ease, upstream can remove redundancies
and further improve checking later.

Reported and initial patches by Demi Marie Obenour.

Fixes: RhBug:1935049, RhBug:1933867, RhBug:1935035, RhBug:1934125, ...

Fixes: CVE-2021-3421, CVE-2021-20271
repository: repo_url: https://github.com/rpm-software-management/rpm
repo_name: rpm-software-management/rpm
description: The RPM package manager
repo_language: C
owner: rpm-software-management
file_changes: filename: package.c
change_type: ModificationType.MODIFY
diff: @@ -31,84 +31,71 @@ struct pkgdata_s {
     rpmRC rc;
 };
 
+struct taglate_s {
+    rpmTagVal stag;
+    rpmTagVal xtag;
+    rpm_count_t count;
+} const xlateTags[] = {
+    { RPMSIGTAG_SIZE, RPMTAG_SIGSIZE, 1 },
+    { RPMSIGTAG_PGP, RPMTAG_SIGPGP, 0 },
+    { RPMSIGTAG_MD5, RPMTAG_SIGMD5, 16 },
+    { RPMSIGTAG_GPG, RPMTAG_SIGGPG, 0 },
+    /* { RPMSIGTAG_PGP5, RPMTAG_SIGPGP5, 0 }, */ /* long obsolete, dont use */
+    { RPMSIGTAG_PAYLOADSIZE, RPMTAG_ARCHIVESIZE, 1 },
+    { RPMSIGTAG_FILESIGNATURES, RPMTAG_FILESIGNATURES, 0 },
+    { RPMSIGTAG_FILESIGNATURELENGTH, RPMTAG_FILESIGNATURELENGTH, 1 },
+    { RPMSIGTAG_VERITYSIGNATURES, RPMTAG_VERITYSIGNATURES, 0 },
+    { RPMSIGTAG_VERITYSIGNATUREALGO, RPMTAG_VERITYSIGNATUREALGO, 1 },
+    { RPMSIGTAG_SHA1, RPMTAG_SHA1HEADER, 1 },
+    { RPMSIGTAG_SHA256, RPMTAG_SHA256HEADER, 1 },
+    { RPMSIGTAG_DSA, RPMTAG_DSAHEADER, 0 },
+    { RPMSIGTAG_RSA, RPMTAG_RSAHEADER, 0 },
+    { RPMSIGTAG_LONGSIZE, RPMTAG_LONGSIGSIZE, 1 },
+    { RPMSIGTAG_LONGARCHIVESIZE, RPMTAG_LONGARCHIVESIZE, 1 },
+    { 0 }
+};
+
 /** \ingroup header
  * Translate and merge legacy signature tags into header.
  * @param h		header (dest)
  * @param sigh		signature header (src)
+ * @return		failing tag number, 0 on success
  */
 static
-void headerMergeLegacySigs(Header h, Header sigh)
+rpmTagVal headerMergeLegacySigs(Header h, Header sigh, char **msg)
 {
-    HeaderIterator hi;
+    const struct taglate_s *xl;
     struct rpmtd_s td;
 
-    hi = headerInitIterator(sigh);
-    for (; headerNext(hi, &td); rpmtdFreeData(&td))
-    {
-	switch (td.tag) {
-	/* XXX Translate legacy signature tag values. */
-	case RPMSIGTAG_SIZE:
-	    td.tag = RPMTAG_SIGSIZE;
-	    break;
-	case RPMSIGTAG_PGP:
-	    td.tag = RPMTAG_SIGPGP;
-	    break;
-	case RPMSIGTAG_MD5:
-	    td.tag = RPMTAG_SIGMD5;
-	    break;
-	case RPMSIGTAG_GPG:
-	    td.tag = RPMTAG_SIGGPG;
-	    break;
-	case RPMSIGTAG_PGP5:
-	    td.tag = RPMTAG_SIGPGP5;
-	    break;
-	case RPMSIGTAG_PAYLOADSIZE:
-	    td.tag = RPMTAG_ARCHIVESIZE;
-	    break;
-	case RPMSIGTAG_FILESIGNATURES:
-	    td.tag = RPMTAG_FILESIGNATURES;
+    rpmtdReset(&td);
+    for (xl = xlateTags; xl->stag; xl++) {
+	/* There mustn't be one in the main header */
+	if (headerIsEntry(h, xl->xtag))
 	    break;
-	case RPMSIGTAG_FILESIGNATURELENGTH:
-	    td.tag = RPMTAG_FILESIGNATURELENGTH;
-	    break;
-	case RPMSIGTAG_VERITYSIGNATURES:
-	case RPMSIGTAG_VERITYSIGNATUREALGO:
-	case RPMSIGTAG_SHA1:
-	case RPMSIGTAG_SHA256:
-	case RPMSIGTAG_DSA:
-	case RPMSIGTAG_RSA:
-	default:
-	    if (!(td.tag >= HEADER_SIGBASE && td.tag < HEADER_TAGBASE))
-		continue;
-	    break;
-	}
-	if (!headerIsEntry(h, td.tag)) {
-	    switch (td.type) {
-	    case RPM_NULL_TYPE:
-		continue;
+	if (headerGet(sigh, xl->stag, &td, HEADERGET_RAW|HEADERGET_MINMEM)) {
+	    /* Translate legacy tags */
+	    if (xl->stag != xl->xtag)
+		td.tag = xl->xtag;
+	    /* Ensure type and tag size match expectations */
+	    if (td.type != rpmTagGetTagType(td.tag))
 		break;
-	    case RPM_CHAR_TYPE:
-	    case RPM_INT8_TYPE:
-	    case RPM_INT16_TYPE:
-	    case RPM_INT32_TYPE:
-	    case RPM_INT64_TYPE:
-		if (td.count != 1)
-		    continue;
+	    if (td.count < 1 || td.count > 16*1024*1024)
 		break;
-	    case RPM_STRING_TYPE:
-	    case RPM_STRING_ARRAY_TYPE:
-	    case RPM_BIN_TYPE:
-		if (td.count >= 16*1024)
-		    continue;
+	    if (xl->count && td.count != xl->count)
 		break;
-	    case RPM_I18NSTRING_TYPE:
-		continue;
+	    if (!headerPut(h, &td, HEADERPUT_DEFAULT))
 		break;
-	    }
-	    (void) headerPut(h, &td, HEADERPUT_DEFAULT);
+	    rpmtdFreeData(&td);
 	}
     }
-    headerFreeIterator(hi);
+    rpmtdFreeData(&td);
+
+    if (xl->stag) {
+	rasprintf(msg, "invalid signature tag %s (%d)",
+			rpmTagGetName(xl->xtag), xl->xtag);
+    }
+
+    return xl->stag;
 }
 
 /**
@@ -380,7 +367,8 @@ rpmRC rpmReadPackageFile(rpmts ts, FD_t fd, const char * fn, Header * hdrp)
 		goto exit;
 
 	    /* Append (and remap) signature tags to the metadata. */
-	    headerMergeLegacySigs(h, sigh);
+	    if (headerMergeLegacySigs(h, sigh, &msg))
+		goto exit;
 	    applyRetrofits(h);
 
 	    /* Bump reference count for return. */

programming_language: C