gpg: Error out on unverified output for non-detached signatures.
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Description

gpg: Error out on unverified output for non-detached signatures.

* g10/mainproc.c (do_proc_packets): Never reset the any.data flag.

Updates-commit: 69384568f66a48eff3968bb1714aa13925580e9f

When using

gpg --verify -o - msg.sig msg

even with the --batch option the outout written to stdout or the file
five to -o may not be what has been verified. For example given a
file "msg" with this content:

--8<---------------cut here---------------start------------->8---
It is a wise father that knows his own child.

William Shakespeare, "The Merchant of Venice"

--8<---------------cut here---------------end--------------->8---

and a manipulated "msg.sig" (named "msg-mod.sig") the output could be

$ gpg --verify -o -  --batch msg-mod.sig msg
The last thing one knows in constructing a work is what to put first.
                -- Blaise Pascal
gpg: Signature made Wed 22 Oct 2025 11:51:52 AM CEST
gpg:                using EDDSA key A7F91C6EB9395B25B4A9BAD25B9[...]
gpg: Good signature from "alice@example.org" [ultimate]

The plaintext shown is ot what has been verified (i.e. the first
quote) and may lead the user top wrong conclusions.

But note: Using the output of the verify command for detached
signatures is useless because with a non-manipulated signature nothing
would haven been written.

How to replicate the whole thing:

Import this public key:

-----BEGIN PGP PUBLIC KEY BLOCK-----
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GjvX

-----END PGP PUBLIC KEY BLOCK-----

Unpack the first quote below and put it into the file "msg"

-----BEGIN PGP ARMORED FILE-----
Comment: Use "gpg --dearmor" for unpacking

SXQgaXMgYSB3aXNlIGZhdGhlciB0aGF0IGtub3dzIGhpcyBvd24gY2hpbGQuCgkJ
LS0gV2lsbGlhbSBTaGFrZXNwZWFyZSwgIlRoZSBNZXJjaGFudCBvZiBWZW5pY2Ui
Cg==

0fUy

-----END PGP ARMORED FILE-----

Unpack the original signature into the file "msg.sig"

-----BEGIN PGP ARMORED FILE-----

iJEEABYKADkWIQSn+RxuuTlbJbSputJbmJ0rJeN/3AUCaPipOBsUgAAAAAAEAA5t
YW51MiwyLjUrMS4xMSwyLDIACgkQW5idKyXjf9w6UwD/fS6X9bs36WXVN5BSANIA
bhtHb8X4jZu4NFKk/ZSwUtIBANMdYO6F1kUMyFNZVZa4Yk12UmcClF9mXLBVlfeH
RFkL

wCLE

-----END PGP ARMORED FILE-----

Unpack the modified signature into the file "msg-mod.sig"

-----BEGIN PGP ARMORED FILE-----

kA0DAAoWW5idKyXjf9wBy19iAGj4qrhUaGUgbGFzdCB0aGluZyBvbmUga25vd3Mg
aW4gY29uc3RydWN0aW5nIGEgd29yayBpcyB3aGF0IHRvIHB1dCBmaXJzdC4KCQkt
LSBCbGFpc2UgUGFzY2FsCoiRBAAWCgA5FiEEp/kcbrk5WyW0qbrSW5idKyXjf9wF
Amj4qTgbFIAAAAAABAAObWFudTIsMi41KzEuMTEsMiwyAAoJEFuYnSsl43/cOlMA
/30ul/W7N+ll1TeQUgDSAG4bR2/F+I2buDRSpP2UsFLSAQDTHWDuhdZFDMhTWVWW
uGJNdlJnApRfZlywVZX3h0RZC8r/AAAAA1BHUA==

DafU

-----END PGP ARMORED FILE-----

Now run

gpg --verify -o -  msg.sig msg
gpg --verify -o -  msg-mod.sig msg

after this pacth is applied the second command will output an error
message "gpg: not a detached signature"

The modification was to prepend a one-pass signature packet for alices
signature and a a literal data packet with the second quote to the
original signature and also append a marker packet or something other.
gpgsplit is the tool of choice here. Thus the packet composition of
msg-mod.sig is:

:onepass_sig packet: keyid 5B989D2B25E37FDC
        version 3, sigclass 0x00, digest 10, pubkey 22, last=1
:literal data packet:
        mode b (62), created 1761127096, name="",
        raw data: 89 bytes
:signature packet: algo 22, keyid 5B989D2B25E37FDC
        version 4, created 1761126712, md5len 0, sigclass 0x00
        [...]
:marker packet: PGP

Kudos to the reporter for the detailed report.