Security Advisories (4)

CVE-2025-40934 (2025-11-26)

XML-Sig versions 0.27 through 0.67 for Perl incorrectly validates XML files if signatures are omitted. An attacker can remove the signature from the XML document to make it pass the verification check. XML-Sig is a Perl module to validate signatures on XML files. An unsigned XML file should return an error message. The affected versions return true when attempting to validate an XML file that contains no signatures.

CVE-2026-18568 (2026-08-03)

XML::Sig versions from 0.29 before 0.72 for Perl allow signature verification bypass because verify returns true when every signature was skipped before any cryptographic check. verify in lib/XML/Sig.pm counts the `//dsig:Signature` elements into `$numsigs` and iterates over them, but two paths reach `next` before any digest or key check runs: a `SignedInfo/Reference/@URI` that resolves to no element while `$numsigs` is greater than 1, and, when `id_attr` is set, a reference that does not match the requested ID. The loop records nothing about what it checked, so when every signature takes one of those paths control reaches the unconditional `return 1` that ends verify. Two `Signature` elements whose Reference URI names an ID that no element carries is enough, as is one such element combined with `id_attr`. Any caller that passes untrusted XML to verify can receive a true return for a document in which no digest and no signature value was checked; a `cert` or `cert_text` trust anchor does not change this, because no key check runs. Versions up to 0.28 use an XML::XPath based verify that has no such skip and are not affected.

CVE-2026-9390 (2026-08-03)

XML::Sig versions before 0.71 for Perl allow XPath injection in ID lookup. verify() and _get_signed_xml() in lib/XML/Sig.pm build XPath expressions by concatenating the SignedInfo/Reference/@URI value read from the document being verified. The value is neither escaped nor checked against the NCName grammar that XML requires of an ID, so a URI containing a single quote closes the string literal in the generated expression and appends arbitrary XPath operators. A crafted URI can make the lookup match elements the reference does not name, or every element in the document, so which node is selected for digest verification is decided by the injected expression rather than by the reference.

CVE-2026-9487 (2026-08-03)

XML::Sig versions before 0.71 for Perl allow signature wrapping via duplicate ID. _get_signed_xml() in lib/XML/Sig.pm, called from verify(), resolves the SignedInfo Reference/@URI to a node with the XPath expression "//*[@ID='$id']" and returns the first node of the resulting node set. A document in which two elements share that ID value is accepted: the digest and signature are checked against whichever element comes first in document order, and the duplicate is not detected. Such a document verifies successfully while an application that resolves the same ID independently can read the second, attacker supplied element; in a SAML2 context this places the contents of an Assertion under attacker control.

NAME

XML::Sig

VERSION

version 0.49

SYNOPSIS

my $xml = '<foo ID="abc">123</foo>';
my $signer = XML::Sig->new({
  key => 'path/to/private.key',
});

# create a signature
my $signed = $signer->sign($xml);
print "Signed XML: $signed\n";

# verify a signature
$signer->verify($signed)
  or die "Signature Invalid.";
print "Signature valid.\n";

DESCRIPTION

This perl module provides two primary capabilities: given an XML string, create and insert digital signatures, or if one is already present in the string verify it -- all in accordance with the W3C standard governing XML signatures.

NAME

XML::Sig - A toolkit to help sign and verify XML Digital Signatures.

PREREQUISITES

USAGE

SUPPORTED ALGORITHMS & TRANSFORMS

This module supports the following signature methods:

DSA
RSA
RSA encoded as x509
ECDSA
ECDSA encoded as x509
HMAC

This module supports the following canonicalization methods and transforms:

Enveloped Signature
REC-xml-c14n-20010315#
REC-xml-c14n-20010315#WithComments
REC-xml-c14n11-20080502
REC-xml-c14n11-20080502#WithComments
xml-exc-c14n#
xml-exc-c14n#WithComments

OPTIONS

Each of the following options are also accessors on the main XML::Sig object. TODO Not strictly correct rewrite

key

The path to a file containing the contents of a private key. This option is used only when generating signatures.

cert

The path to a file containing a PEM-formatted X509 certificate. This option is used only when generating signatures with the "x509" option. This certificate will be embedded in the signed document, and should match the private key used for the signature.

cert_text

A string containing a PEM-formatted X509 certificate. This option is used only when generating signatures with the "x509" option. This certificate will be embedded in the signed document, and should match the private key used for the signature.

x509

Takes a true (1) or false (0) value and indicates how you want the signature to be encoded. When true, the X509 certificate supplied will be encoded in the signature. Otherwise the native encoding format for RSA, DSA and ECDSA will be used.

sig_hash

Passing sig_hash to new allows you to specify the SignatureMethod hashing algorithm used when signing the SignedInfo. RSA and ECDSA supports the hashes specified sha1, sha224, sha256, sha384 and sha512

DSA supports only sha1 and sha256 (but you really should not sign anything with DSA anyway).

digest_hash

Passing digest_hash to new allows you to specify the DigestMethod hashing algorithm used when calculating the hash of the XML being signed. Supported hashes can be specified sha1, sha224, sha256, sha384, and sha512

hmac_key

Base64 encoded hmac_key

no_xml_declaration

Some applications such as Net::SAML2 expect to sign a fragment of the full XML document so is this is true (1) it will not include the XML Declaration at the beginning of the signed XML. False (0) or undefined returns an XML document starting with the XML Declaration.

METHODS

new(...)

Constructor; see OPTIONS above.

sign($xml)

When given a string of XML, it will return the same string with a signature generated from the key provided when the XML::Sig object was initialized.

This method will sign all elements in your XML with an ID (case sensitive) attribute. Each element with an ID attribute will be the basis for a seperate signature. It will correspond to the URI attribute in the Reference element that will be contained by the signature. If no ID attribute can be found on an element, the signature will not be created.

The elements are signed in reverse order currently assuming (possibly incorrectly) that the lower element in the tree may need to be signed inclusive of its Signature because it is a child of the higher element.

Arguments: $xml: string XML string

Returns: string Signed XML

verify($xml)

Returns true or false based upon whether the signature is valid or not.

When using XML::Sig exclusively to verify a signature, no key needs to be specified during initialization given that the public key should be transmitted with the signature.

XML::Sig checks all signature in the provided xml and will fail should any signature pointing to an existing ID in the XML fail to verify.

Should there be a Signature included that does not point to an existing node in the XML it is ignored and other Signaures are checked. If there are no other Signatures it will return false.

Arguments: $xml: string XML string

Returns: string Signed XML

signer_cert()

Following a successful verify with an X509 certificate, returns the signer's certificate as embedded in the XML document for verification against a CA certificate. The certificate is returned as a Crypt::OpenSSL::X509 object.

Arguments: none

Returns: Crypt::OpenSSL::X509: Certificate used to sign the XML

ABOUT DIGITAL SIGNATURES

Just as one might want to send an email message that is cryptographically signed in order to give the recipient the means to independently verify who sent the email, one might also want to sign an XML document. This is especially true in the scenario where an XML document is received in an otherwise unauthenticated context, e.g. SAML.

However XML provides a challenge that email does not. In XML, two documents can be byte-wise inequivalent, and semanticaly equivalent at the same time. For example:

<?xml version="1.0"?>
<foo>
  <bar />
</foo>

And:

<?xml version="1.0"?>
<foo>
  <bar></bar>
</foo>

Each of these document express the same thing, or in other words they "mean" the same thing. However if you were to strictly sign the raw text of these documents, they would each produce different signatures.

XML Signatures on the other hand will produce the same signature for each of the documents above. Therefore an XML document can be written and rewritten by different parties and still be able to have someone at the end of the line verify a signature the document may contain.

There is a specially subscribed methodology for how this process should be executed and involves transforming the XML into its canonical form so a signature can be reliably inserted or extracted for verification. This module implements that process.

EXAMPLE SIGNATURE

Below is a sample XML signature to give you some sense of what they look like. First let's look at the original XML document, prior to being signed:

<?xml version="1.0"?>
<foo ID="abc">
  <bar>123</bar>
</foo>

Now, let's insert a signature:

<?xml version="1.0"?>
<foo ID="abc">
  <bar>123</bar>
  <Signature xmlns="http://www.w3.org/2000/09/xmldsig#">
    <SignedInfo xmlns="http://www.w3.org/2000/09/xmldsig#" xmlns:samlp="urn:oasis:names:tc:SAML:2.0:protocol" xmlns:xenc="http://www.w3.org/2001/04/xmlenc#">
      <CanonicalizationMethod Algorithm="http://www.w3.org/TR/2001/REC-xml-c14n-20010315#WithComments" />
      <SignatureMethod Algorithm="http://www.w3.org/2000/09/xmldsig#rsa-sha1" />
      <Reference URI="#abc">
        <Transforms>
          <Transform Algorithm="http://www.w3.org/2000/09/xmldsig#enveloped-signature" />
        </Transforms>
        <DigestMethod Algorithm="http://www.w3.org/2000/09/xmldsig#sha1" />
        <DigestValue>9kpmrvv3peVJpNSTRycrV+jeHVY=</DigestValue>
      </Reference>
    </SignedInfo>
    <SignatureValue>
      HXUBnMgPJf//j4ihaWnaylNwAR5AzDFY83HljFIlLmTqX1w1C72ZTuRObvYve8TNEbVsQlTQkj4R
      hiY0pgIMQUb75GLYFtc+f0YmBZf5rCWY3NWzo432D3ogAvpEzYXEQPmicWe2QozQhybaz9/wrYki
      XiXY+57fqCkf7aT8Bb6G+fn7Aj8gnZFLkmKxwCdyGsIZOIZdQ8MWpeQrifxBR0d8W1Zm6ix21WNv
      ONt575h7VxLKw8BDhNPS0p8CS3hOnSk29stpiDMCHFPxAwrbKVL1kGDLaLZn1q8nNRmH8oFxG15l
      UmS3JXDZAss8gZhU7g9T4XllCqjrAvzPLOFdeQ==
    </SignatureValue>
    <KeyInfo>
      <KeyValue>
        <RSAKeyValue>
          <Modulus>
            1b+m37u3Xyawh2ArV8txLei251p03CXbkVuWaJu9C8eHy1pu87bcthi+T5WdlCPKD7KGtkKn9vq
            i4BJBZcG/Y10e8KWVlXDLg9gibN5hb0Agae3i1cCJTqqnQ0Ka8w1XABtbxTimS1B0aO1zYW6d+U
            Yl0xIeAOPsGMfWeu1NgLChZQton1/NrJsKwzMaQy1VI8m4gUleit9Z8mbz9bNMshdgYEZ9oC4bH
            n/SnA4FvQl1fjWyTpzL/aWF/bEzS6Qd8IBk7yhcWRJAGdXTWtwiX4mXb4h/2sdrSNvyOsd/shCf
            OSMsf0TX+OdlbH079AsxOwoUjlzjuKdCiFPdU6yAJw==
          </Modulus>
          <Exponent>Iw==</Exponent>
        </RSAKeyValue>
      </KeyValue>
    </KeyInfo>
  </Signature>
</foo>

VERSION CONTROL

https://github.com/perl-net-saml2/perl-XML-Sig

AUTHORS and CREDITS

Author: Byrne Reese <byrne@majordojo.com>

Thanks to Manni Heumann who wrote Google::SAML::Response from which this module borrows heavily in order to create digital signatures.

Net::SAML2 embedded version amended by Chris Andrews <chris@nodnol.org>.

Maintainer: Timothy Legge <timlegge@cpan.org>

AUTHORS

Byrne Reese <byrne@cpan.org>
Timothy Legge <timlegge@cpan.org>

COPYRIGHT AND LICENSE

Copyright 2009       Byrne, Michael Hendricks
          2010       Chris Andrews
          2011       Chris Andrews, Oskari Okko Ojala
          2012       Chris Andrews, Peter Marschall
          2015       Mike Wisener
          2016       Jeff Fearn
          2017       Mike Wisener, xmikew
          2019-2021  Timothy Legge

This is free software; you can redistribute it and/or modify it under the same terms as the Perl 5 programming language system itself.

To install XML::Sig, copy and paste the appropriate command in to your terminal.

cpanm

cpanm XML::Sig

CPAN shell

perl -MCPAN -e shell
install XML::Sig

For more information on module installation, please visit the detailed CPAN module installation guide.

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NAME

VERSION

SYNOPSIS

DESCRIPTION

NAME

PREREQUISITES

USAGE

SUPPORTED ALGORITHMS & TRANSFORMS

OPTIONS

METHODS

new(...)

sign($xml)

verify($xml)

signer_cert()

ABOUT DIGITAL SIGNATURES

EXAMPLE SIGNATURE

SEE ALSO

VERSION CONTROL

AUTHORS and CREDITS

AUTHORS

COPYRIGHT AND LICENSE

Module Install Instructions

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